Oracle Linux 6 STIG
Oracle Linux 6 Security Technical Implementation Guide. Version v2 r5, released Oct. 27, 2021.
OL6-00-000527: The login user list must be disabled.
If the GConf2 package is not installed, this is not applicable. To ensure the user list is disabled, run the following command: $ gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --get /apps/gdm/simple-greeter/disable_user_list The output should be "true". If it is not, this is a finding.
Discussion
Leaving the user list enabled is a security risk since it allows anyone with physical access to the system to quickly enumerate known user accounts without logging in.
Fix
In the default graphical environment, users logging directly into the system are greeted with a login screen that displays all known users. This functionality should be disabled. Run the following command to disable the user list: $ sudo gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type bool --set /apps/gdm/simple-greeter/disable_user_list true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209070r603263_rule'
OL6-00-000145: The operating system must produce audit records containing sufficient information to establish the identity of any user/subject associated with the event.
Run the following command to determine the current status of the "auditd" service: # service auditd status If the service is enabled, it should return the following: auditd is running... If the service is not running, this is a finding.
Discussion
Ensuring the "auditd" service is active ensures audit records generated by the kernel can be written to disk, or that appropriate actions will be taken if other obstacles exist.
Fix
The "auditd" service is an essential userspace component of the Linux Auditing System, as it is responsible for writing audit records to disk. The "auditd" service can be enabled with the following commands: # chkconfig auditd on # service auditd start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208875r603263_rule'
OL6-00-000084: The system must not accept ICMPv4 redirect packets on any interface.
The status of the "net.ipv4.conf.all.accept_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.accept_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.all.accept_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Accepting ICMP redirects has few legitimate uses. It should be disabled unless it is absolutely required.
Fix
To set the runtime status of the "net.ipv4.conf.all.accept_redirects" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.accept_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.accept_redirects = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208854r603263_rule'
OL6-00-000008: Vendor-provided cryptographic certificates must be installed to verify the integrity of system software.
To ensure that the GPG key is installed, run: # rpm -qi gpg-pubkey-ec551f03 | gpg --keyid-format long | grep oracle.com | cut -f3 -d" " |cut -f2 -d"/" The command should return the string below: 72F97B74EC551F03 If the operating system vendor GPG Key is not installed, this is a finding.
Discussion
This key is necessary to cryptographically verify packages that packages are from the operating system vendor.
Fix
To ensure the system can cryptographically verify the software packages come from the operating system vendor (and connect to the vendor's network software repository to receive them if desired), the vendor GPG key must properly be installed. To ensure the GPG key is installed, run: # wget http://public-yum.oracle.com/RPM-GPG-KEY-oracle-ol6 # rpm --import RPM-GPG-KEY-oracle-ol6
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-219543r603263_rule'
OL6-00-000080: The system must not send ICMPv4 redirects by default.
The status of the "net.ipv4.conf.default.send_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.default.send_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.default.send_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Sending ICMP redirects permits the system to instruct other systems to update their routing information. The ability to send ICMP redirects is only appropriate for systems acting as routers.
Fix
To set the runtime status of the "net.ipv4.conf.default.send_redirects" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.default.send_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.default.send_redirects = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208850r603263_rule'
OL6-00-000343: The system default umask for the csh shell must be 077.
Verify the "umask" setting is configured correctly in the "/etc/csh.cshrc" file by running the following command: # grep "umask" /etc/csh.cshrc All output must show the value of "umask" set to 077, as shown in the below: # grep "umask" /etc/csh.cshrc umask 077 If the above command returns no output, or if the umask is configured incorrectly, this is a finding.
Discussion
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and/or written to by unauthorized users.
Fix
To ensure the default umask for users of the C shell is set properly, add or correct the "umask" setting in "/etc/csh.cshrc" to read as follows: umask 077
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209045r603263_rule'
OL6-00-000194: The audit system must be configured to audit all discretionary access control permission modifications using lsetxattr.
To determine if the system is configured to audit calls to the "lsetxattr" system call, run the following command: $ sudo grep -w "lsetxattr" /etc/audit/audit.rules -a always,exit -F arch=b32 -S lsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S lsetxattr -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S lsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S lsetxattr -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "lsetxattr" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S lsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S lsetxattr -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S lsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S lsetxattr -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208903r603263_rule'
OL6-00-000289: The netconsole service must be disabled unless required.
To check that the "netconsole" service is disabled in system boot configuration, run the following command: # chkconfig "netconsole" --list Output should indicate the "netconsole" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "netconsole" --list "netconsole" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "netconsole" is disabled through current runtime configuration: # service netconsole status If the service is disabled the command will return the following output: netconsole is stopped If the service is running, this is a finding.
Discussion
The "netconsole" service is not necessary unless there is a need to debug kernel panics, which is not common.
Fix
The "netconsole" service is responsible for loading the netconsole kernel module, which logs kernel printk messages over UDP to a syslog server. This allows debugging of problems where disk logging fails and serial consoles are impractical. The "netconsole" service can be disabled with the following commands: # chkconfig netconsole off # service netconsole stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209022r603263_rule'
OL6-00-000015: The system package management tool must cryptographically verify the authenticity of all software packages during installation.
To determine whether "yum" has been configured to disable "gpgcheck" for any repos, inspect all files in "/etc/yum.repos.d" and ensure the following does not appear in any sections: gpgcheck=0 A value of "0" indicates that "gpgcheck" has been disabled for that repo. If GPG checking is disabled, this is a finding. If the "yum" system package management tool is not used to update the system, verify with the SA that installed packages are cryptographically signed.
Discussion
Ensuring all packages' cryptographic signatures are valid prior to installation ensures the provenance of the software and protects against malicious tampering.
Fix
To ensure signature checking is not disabled for any repos, remove any lines from files in "/etc/yum.repos.d" of the form: gpgcheck=0
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219545r603263_rule'
OL6-00-000236: The SSH daemon must not allow host-based authentication.
To determine how the SSH daemon's "HostbasedAuthentication" option is set, run the following command: # grep -i HostbasedAuthentication /etc/ssh/sshd_config If no line, a commented line, or a line indicating the value "no" is returned, then the required value is set. If the required value is not set, this is a finding.
Discussion
SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.
Fix
SSH's cryptographic host-based authentication is more secure than ".rhosts" authentication, since hosts are cryptographically authenticated. However, it is not recommended that hosts unilaterally trust one another, even within an organization. To disable host-based authentication, add or correct the following line in "/etc/ssh/sshd_config": HostbasedAuthentication no
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208924r603263_rule'
OL6-00-000275: The operating system must employ cryptographic mechanisms to protect information in storage.
Determine if encryption must be used to protect data on the system. If encryption must be used and is not employed, this is a finding.
Discussion
The risk of a system's physical compromise, particularly mobile systems such as laptops, places its data at risk of compromise. Encrypting this data mitigates the risk of its loss if the system is lost.
Fix
The operating system natively supports partition encryption through the Linux Unified Key Setup (LUKS) on-disk-format technology. The easiest way to encrypt a partition is during installation time. For manual installations, select the "Encrypt" checkbox during partition creation to encrypt the partition. When this option is selected, the system will prompt for a passphrase to use in decrypting the partition. The passphrase will subsequently need to be entered manually every time the system boots. For automated/unattended installations, it is possible to use Kickstart by adding the "--encrypted" and "--passphrase=" options to the definition of each partition to be encrypted. For example, the following line would encrypt the root partition: part / --fstype=ext3 --size=100 --onpart=hda1 --encrypted --passphrase=[PASSPHRASE] Any [PASSPHRASE] is stored in the Kickstart in plaintext, and the Kickstart must then be protected accordingly. Omitting the "--passphrase=" option from the partition definition will cause the installer to pause and interactively ask for the passphrase during installation. Detailed information on encrypting partitions using LUKS can be found in the Oracle Linux documentation at: http://docs.oracle.com/cd/E37670_01/E36387/html/index.html Additional information is available from: http://linux.oracle.com/documentation/OL6/Red_Hat_Enterprise_Linux-6-Security_Guide-en-US.pdf
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219566r603263_rule'
OL6-00-000347: There must be no .netrc files on the system.
To check the system for the existence of any ".netrc" files, run the following command: $ sudo find /root /home -xdev -name .netrc If any .netrc files exist, this is a finding.
Discussion
Unencrypted passwords for remote FTP servers may be stored in ".netrc" files. DoD policy requires passwords be encrypted in storage and not used in access scripts.
Fix
The ".netrc" files contain login information used to auto-login into FTP servers and reside in the user's home directory. These files may contain unencrypted passwords to remote FTP servers making them susceptible to access by unauthorized users and should not be used. Any ".netrc" files should be removed.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209049r603263_rule'
OL6-00-000240: The SSH daemon must be configured with the Department of Defense (DoD) login banner.
To determine how the SSH daemon's "Banner" option is set, run the following command: # grep -i Banner /etc/ssh/sshd_config If a line indicating /etc/issue is returned, then the required value is set. If the required value is not set, this is a finding.
Discussion
The warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers. Alternatively, systems whose ownership should not be obvious should ensure usage of a banner that does not provide easy attribution.
Fix
To enable the warning banner and ensure it is consistent across the system, add or correct the following line in "/etc/ssh/sshd_config": Banner /etc/issue Another section contains information on how to create an appropriate system-wide warning banner.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208927r603263_rule'
OL6-00-000186: The audit system must be configured to audit all discretionary access control permission modifications using fchmod.
To determine if the system is configured to audit calls to the "fchmod" system call, run the following command: $ sudo grep -w "fchmod" /etc/audit/audit.rules -a always,exit -F arch=b32 -S fchmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchmod -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S fchmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchmod -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "fchmod" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S fchmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchmod -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S fchmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchmod -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208895r603263_rule'
OL6-00-000120: The systems local IPv4 firewall must implement a deny-all, allow-by-exception policy for inbound packets.
Inspect the file "/etc/sysconfig/iptables" to determine the default policy for the INPUT chain. It should be set to DROP. # grep ":INPUT" /etc/sysconfig/iptables If the default policy for the INPUT chain is not set to DROP, this is a finding.
Discussion
In "iptables" the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to "DROP" implements proper design for a firewall, i.e., any packets which are not explicitly permitted should not be accepted.
Fix
To set the default policy to DROP (instead of ACCEPT) for the built-in INPUT chain which processes incoming packets, add or correct the following line in "/etc/sysconfig/iptables": :INPUT DROP [0:0]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219554r603263_rule'
OL6-00-000303: The operating system must employ automated mechanisms, per organization defined frequency, to detect the addition of unauthorized components/devices into the operating system.
To determine that periodic AIDE execution has been scheduled, run the following command: # grep aide /etc/crontab /etc/cron.*/* If there is no output, this is a finding.
Discussion
By default, AIDE does not install itself for periodic execution. Periodically running AIDE may reveal unexpected changes in installed files.
Fix
AIDE should be executed on a periodic basis to check for changes. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check AIDE can be executed periodically through other means; this is merely one example.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219572r603263_rule'
OL6-00-000287: The postfix service must be enabled for mail delivery.
Run the following command to determine the current status of the "postfix" service: # service postfix status If the service is enabled, it should return the following: postfix is running... If the service is not enabled, this is a finding.
Discussion
Local mail delivery is essential to some system maintenance and notification tasks.
Fix
The Postfix mail transfer agent is used for local mail delivery within the system. The default configuration only listens for connections to the default SMTP port (port 25) on the loopback interface (127.0.0.1). It is recommended to leave this service enabled for local mail delivery. The "postfix" service can be enabled with the following command: # chkconfig postfix on # service postfix start
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209020r603263_rule'
OL6-00-000174: The operating system must automatically audit account creation.
To determine if the system is configured to audit account changes, run the following command: $ sudo egrep -w '(/etc/passwd|/etc/shadow|/etc/group|/etc/gshadow|/etc/security/opasswd)' /etc/audit/audit.rules If the system is configured to watch for account changes, lines should be returned for each file specified (and with "-p wa" for each). If the system is not configured to audit account changes, this is a finding.
Discussion
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
Fix
Add the following to "/etc/audit/audit.rules", in order to capture events that modify account changes: # audit_account_changes -w /etc/group -p wa -k audit_account_changes -w /etc/passwd -p wa -k audit_account_changes -w /etc/gshadow -p wa -k audit_account_changes -w /etc/shadow -p wa -k audit_account_changes -w /etc/security/opasswd -p wa -k audit_account_changes
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208887r603263_rule'
OL6-00-000190: The audit system must be configured to audit all discretionary access control permission modifications using fremovexattr.
To determine if the system is configured to audit calls to the "fremovexattr" system call, run the following command: $ sudo grep -w "fremovexattr" /etc/audit/audit.rules -a always,exit -F arch=b32 -S fremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fremovexattr -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S fremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fremovexattr -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "fremovexattr" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S fremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fremovexattr -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S fremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fremovexattr -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208899r603263_rule'
OL6-00-000239: The SSH daemon must not allow authentication using an empty password.
To determine how the SSH daemon's "PermitEmptyPasswords" option is set, run the following command: # grep -i PermitEmptyPasswords /etc/ssh/sshd_config If no line, a commented line, or a line indicating the value "no" is returned, then the required value is set. If the required value is not set, this is a finding.
Discussion
Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.
Fix
To explicitly disallow remote login from accounts with empty passwords, add or correct the following line in "/etc/ssh/sshd_config": PermitEmptyPasswords no Any accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords.
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-208926r603263_rule'
OL6-00-000113: The system must employ a local IPv4 firewall.
If the system is a cross-domain system, this is not applicable. Run the following command to determine the current status of the "iptables" service: # service iptables status If the service is not running, it should return the following: iptables: Firewall is not running. If the service is not running, this is a finding.
Discussion
The "iptables" service provides the system's host-based firewalling capability for IPv4 and ICMP.
Fix
The "iptables" service can be enabled with the following commands: # chkconfig iptables on # service iptables start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219551r603263_rule'
OL6-00-000220: The ypserv package must not be installed.
Run the following command to determine if the "ypserv" package is installed: # rpm -q ypserv If the package is installed, this is a finding.
Discussion
Removing the "ypserv" package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services.
Fix
The "ypserv" package can be uninstalled with the following command: # yum erase ypserv
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208917r603263_rule'
OL6-00-000279: The system package management tool must verify ownership on all files and directories associated with the audit package.
The following command will list which audit files on the system have ownership different from what is expected by the RPM database: # rpm -V audit | grep '^.....U' If there is output, this is a finding.
Discussion
Ownership of audit binaries and configuration files that is incorrect could allow an unauthorized user to gain privileges that they should not have. The ownership set by the vendor should be maintained. Any deviations from this baseline should be investigated.
Fix
The RPM package management system can restore file ownership of the audit package files and directories. The following command will update audit files with ownership different from what is expected by the RPM database: # rpm --setugids audit
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209015r603263_rule'
OL6-00-000272: The system must use SMB client signing for connecting to samba servers using smbclient.
To verify that Samba clients running smbclient must use packet signing, run the following command: # grep signing /etc/samba/smb.conf The output should show: client signing = mandatory If it is not, this is a finding.
Discussion
Packet signing can prevent man-in-the-middle attacks which modify SMB packets in transit.
Fix
To require samba clients running "smbclient" to use packet signing, add the following to the "[global]" section of the Samba configuration file in "/etc/samba/smb.conf": client signing = mandatory Requiring samba clients such as "smbclient" to use packet signing ensures they can only communicate with servers that support packet signing.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209010r603263_rule'
OL6-00-000097: The system must use a reverse-path filter for IPv4 network traffic when possible by default.
The status of the "net.ipv4.conf.default.rp_filter" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.default.rp_filter The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.default.rp_filter /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.
Fix
To set the runtime status of the "net.ipv4.conf.default.rp_filter" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.default.rp_filter=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.default.rp_filter = 1
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208864r603263_rule'
OL6-00-000002: The system must use a separate file system for /var.
Run the following command to determine if "/var" is on its own partition or logical volume: $ mount | grep "on /var " If "/var" has its own partition or volume group, a line will be returned. If no line is returned, this is a finding.
Discussion
Ensuring that "/var" is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the "/var" directory to contain world-writable directories, installed by other software packages.
Fix
The "/var" directory is used by daemons and other system services to store frequently-changing data. Ensure that "/var" has its own partition or logical volume at installation time, or migrate it using LVM.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208794r603263_rule'
OL6-00-000523: The systems local IPv6 firewall must implement a deny-all, allow-by-exception policy for inbound packets.
If IPv6 is disabled, this is not applicable. Inspect the file "/etc/sysconfig/ip6tables" to determine the default policy for the INPUT chain. It should be set to DROP: # grep ":INPUT" /etc/sysconfig/ip6tables If the default policy for the INPUT chain is not set to DROP, this is a finding.
Discussion
In "ip6tables" the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to "DROP" implements proper design for a firewall, i.e., any packets which are not explicitly permitted should not be accepted.
Fix
To set the default policy to DROP (instead of ACCEPT) for the built-in INPUT chain which processes incoming packets, add or correct the following line in "/etc/sysconfig/ip6tables": :INPUT DROP [0:0] Restart the IPv6 firewall: # service ip6tables restart
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219588r603263_rule'
OL6-00-000133: All rsyslog-generated log files must be owned by root.
The owner of all log files written by "rsyslog" should be root. These log files are determined by the second part of each Rule line in "/etc/rsyslog.conf" and typically all appear in "/var/log". To see the owner of a given log file, run the following command: $ ls -l [LOGFILE] Some log files referenced in /etc/rsyslog.conf may be created by other programs and may require exclusion from consideration. If the owner is not root, this is a finding.
Discussion
The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
Fix
The owner of all log files written by "rsyslog" should be root. These log files are determined by the second part of each Rule line in "/etc/rsyslog.conf" typically all appear in "/var/log". For each log file [LOGFILE] referenced in "/etc/rsyslog.conf", run the following command to inspect the file's owner: $ ls -l [LOGFILE] If the owner is not "root", run the following command to correct this: # chown root [LOGFILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208870r603263_rule'
OL6-00-000293: Wireless network adapters must be disabled.
This is N/A for systems that do not have wireless network adapters. Verify that there are no wireless interfaces configured on the system: # ifconfig -a eth0 Link encap:Ethernet HWaddr b8:ac:6f:65:31:e5 inet addr:192.168.2.100 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::baac:6fff:fe65:31e5/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2697529 errors:0 dropped:0 overruns:0 frame:0 TX packets:2630541 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2159382827 (2.0 GiB) TX bytes:1389552776 (1.2 GiB) Interrupt:17 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:2849 errors:0 dropped:0 overruns:0 frame:0 TX packets:2849 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2778290 (2.6 MiB) TX bytes:2778290 (2.6 MiB) If a wireless interface is configured, it must be documented and approved by the local Authorizing Official. If a wireless interface is configured and has not been documented and approved, this is a finding.
Discussion
The use of wireless networking can introduce many different attack vectors into the organization’s network. Common attack vectors such as malicious association and ad hoc networks will allow an attacker to spoof a wireless access point (AP), allowing validated systems to connect to the malicious AP and enabling the attacker to monitor and record network traffic. These malicious APs can also serve to create a man-in-the-middle attack or be used to create a denial of service to valid network resources.
Fix
Configure the system to disable all wireless network interfaces.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219570r603263_rule'
OL6-00-000061: The system must disable accounts after three consecutive unsuccessful logon attempts.
To ensure the failed password attempt policy is configured correctly, run the following command: # grep pam_faillock /etc/pam.d/system-auth /etc/pam.d/password-auth The output should show "deny=3" for both files. If that is not the case, this is a finding.
Discussion
Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks.
Fix
To configure the system to lock out accounts after a number of incorrect logon attempts using "pam_faillock.so", modify the content of both "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" as follows: Add the following line immediately before the "pam_unix.so" statement in the "AUTH" section: auth required pam_faillock.so preauth silent deny=3 unlock_time=900 fail_interval=900 Add the following line immediately after the "pam_unix.so" statement in the "AUTH" section: auth [default=die] pam_faillock.so authfail deny=3 unlock_time=900 fail_interval=900 Add the following line immediately before the "pam_unix.so" statement in the "ACCOUNT" section: account required pam_faillock.so Note that any updates made to "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" may be overwritten by the "authconfig" program. The "authconfig" program should not be used.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208836r603263_rule'
OL6-00-000011: System security patches and updates must be installed and up-to-date.
If the system is joined to Oracle's Unbreakable Linux Network or an internal YUM server that provides updates, invoking the following command will indicate if updates are available.: # yum check-update If the system is not configured to update from one of these sources, run the following command to list when each package was last updated: $ rpm -qa -last Compare this to (1) http://linux.oracle.com/errata/ and (2) http://linux.oracle.com/cve/ to determine if the system is missing applicable security and bugfix updates. If updates are not installed, this is a finding. A ULN account is not required to obtain security updates Oracle also makes this content freely available on its Public YUM server at: http://public-yum.oracle.com/.
Discussion
Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities.
Fix
If the system is joined to Oracle's Unbreakable Linux Network or an internal YUM server, run the following command to install updates # yum update If the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from Oracle's Unbreakable Linux Network and installed using the "rpm" command.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208798r603263_rule'
OL6-00-000025: All device files must be monitored by the system Linux Security Module.
To check for unlabeled device files, run the following command: # ls -RZ /dev | grep unlabeled_t It should produce no output in a well-configured system. If there is output, this is a finding.
Discussion
If a device file carries the SELinux type "unlabeled_t", then SELinux cannot properly restrict access to the device file.
Fix
Device files, which are used for communication with important system resources, should be labeled with proper SELinux types. If any device files carry the SELinux type "unlabeled_t", investigate the cause and correct the file's context.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208803r603263_rule'
OL6-00-000339: The FTP daemon must be configured for logging or verbose mode.
Verify the "vsftpd" package is installed: # rpm -qa | grep -i vsftpd vsftpd-3.0.2-22.e16.x86_64 If the "vsftpd" package is not installed, this is Not Applicable. Find if logging is applied to the ftp daemon. Procedures: If vsftpd is started by xinetd the following command will indicate the xinetd.d startup file. # grep vsftpd /etc/xinetd.d/* # grep server_args [vsftpd xinetd.d startup file] This will indicate the vsftpd config file used when starting through xinetd. If the [server_args]line is missing or does not include the vsftpd configuration file, then the default config file (/etc/vsftpd/vsftpd.conf) is used. # grep xferlog_enable [vsftpd config file] If xferlog_enable is missing, or is not set to yes, this is a finding.
Discussion
To trace malicious activity facilitated by the FTP service, it must be configured to ensure that all commands sent to the ftp server are logged using the verbose vsftpd log format. The default vsftpd log file is /var/log/vsftpd.log.
Fix
Add or correct the following configuration options within the "vsftpd" configuration file, located at "/etc/vsftpd/vsftpd.conf". xferlog_enable=YES xferlog_std_format=NO log_ftp_protocol=YES
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209041r603263_rule'
OL6-00-000184: The audit system must be configured to audit all discretionary access control permission modifications using chmod.
To determine if the system is configured to audit calls to the "chmod" system call, run the following command: $ sudo grep -w "chmod" /etc/audit/audit.rules -a always,exit -F arch=b32 -S chmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S chmod -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S chmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S chmod -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "chmod" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S chmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S chmod -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S chmod -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S chmod -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208893r603263_rule'
OL6-00-000028: The system must prevent the root account from logging in from serial consoles.
To check for serial port entries which permit root login, run the following command: # grep '^ttyS[0-9]' /etc/securetty If any output is returned, then root login over serial ports is permitted. If root login over serial ports is permitted, this is a finding.
Discussion
Preventing direct root login to serial port interfaces helps ensure accountability for actions taken on the systems using the root account.
Fix
To restrict root logins on serial ports, ensure lines of this form do not appear in "/etc/securetty": ttyS0 ttyS1 Note: Serial port entries are not limited to those listed above. Any lines starting with "ttyS" followed by numerals should be removed.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208805r603263_rule'
OL6-00-000530: The Oracle Linux operating system must mount /dev/shm with the nodev option.
Verify that the "nodev" option is configured for /dev/shm. Check that the operating system is configured to use the "nodev" option for /dev/shm with the following command: # cat /etc/fstab | grep /dev/shm | grep nodev tmpfs /dev/shm tmpfs defaults,nodev,nosuid,noexec 0 0 If the "nodev" option is not present on the line for "/dev/shm", this is a finding. Verify "/dev/shm" is mounted with the "nodev" option: # mount | grep "/dev/shm" | grep nodev If no results are returned, this is a finding.
Discussion
The "nodev" mount option causes the system to not interpret character or block special devices. Executing character or block special devices from untrusted file systems increases the opportunity for unprivileged users to attain unauthorized administrative access.
Fix
Configure the "/etc/fstab" to use the "nodev" option for all lines containing "/dev/shm".
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209073r603263_rule'
OL6-00-000063: The system must use a FIPS 140-2 approved cryptographic hashing algorithm for generating account password hashes (login.defs).
Inspect "/etc/login.defs" and ensure the following line appears: ENCRYPT_METHOD SHA512 If it does not, this is a finding.
Discussion
Using a stronger hashing algorithm makes password cracking attacks more difficult.
Fix
In "/etc/login.defs", add or correct the following line to ensure the system will use SHA-512 as the hashing algorithm: ENCRYPT_METHOD SHA512
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208838r603263_rule'
OL6-00-000001: The system must use a separate file system for /tmp.
Run the following command to determine if "/tmp" is on its own partition or logical volume: $ mount | grep "on /tmp " If "/tmp" has its own partition or volume group, a line will be returned. If no line is returned, this is a finding.
Discussion
The "/tmp" partition is used as temporary storage by many programs. Placing "/tmp" in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.
Fix
The "/tmp" directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208793r603263_rule'
OL6-00-000307: The operating system must ensure unauthorized, security-relevant configuration changes detected are tracked.
To determine that periodic AIDE execution has been scheduled, run the following command: # grep aide /etc/crontab /etc/cron.*/* If there is no output, this is a finding.
Discussion
By default, AIDE does not install itself for periodic execution. Periodically running AIDE may reveal unexpected changes in installed files.
Fix
AIDE should be executed on a periodic basis to check for changes. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check AIDE can be executed periodically through other means; this is merely one example.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219576r603263_rule'
OL6-00-000039: The /etc/passwd file must be owned by root.
To check the ownership of "/etc/passwd", run the command: $ ls -l /etc/passwd If properly configured, the output should indicate the following owner: "root" If it does not, this is a finding.
Discussion
The "/etc/passwd" file contains information about the users that are configured on the system. Protection of this file is critical for system security.
Fix
To properly set the owner of "/etc/passwd", run the command: # chown root /etc/passwd
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208816r603263_rule'
OL6-00-000206: The telnet-server package must not be installed.
Run the following command to determine if the "telnet-server" package is installed: # rpm -q telnet-server If the package is installed, this is a finding.
Discussion
Removing the "telnet-server" package decreases the risk of the unencrypted telnet service's accidental (or intentional) activation. Mitigation: If the telnet-server package is configured to only allow encrypted sessions, such as with Kerberos or the use of encrypted network tunnels, the risk of exposing sensitive information is mitigated.
Fix
The "telnet-server" package can be uninstalled with the following command: # yum erase telnet-server
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-208913r603263_rule'
OL6-00-000258: The graphical desktop environment must automatically lock after 15 minutes of inactivity and the system must require user reauthentication to unlock the environment.
If the GConf2 package is not installed, this is not applicable. To check the screensaver mandatory use status, run the following command: $ gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gnome-screensaver/idle_activation_enabled If properly configured, the output should be "true". If it is not, this is a finding.
Discussion
Enabling idle activation of the screen saver ensures the screensaver will be activated after the idle delay. Applications requiring continuous, real-time screen display (such as network management products) require the login session does not have administrator rights and the display station is located in a controlled-access area.
Fix
Run the following command to activate the screensaver in the GNOME desktop after a period of inactivity: # gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type bool \ --set /apps/gnome-screensaver/idle_activation_enabled true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208934r603263_rule'
OL6-00-000103: The system must employ a local IPv6 firewall.
If the system is a cross-domain system, this is not applicable. If IPv6 is disabled, this is not applicable. Run the following command to determine the current status of the "ip6tables" service: # service ip6tables status If the service is not running, it should return the following: ip6tables: Firewall is not running. If the service is not running, this is a finding.
Discussion
The "ip6tables" service provides the system's host-based firewalling capability for IPv6 and ICMPv6.
Fix
The "ip6tables" service can be enabled with the following commands: # chkconfig ip6tables on # service ip6tables start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219548r603263_rule'
OL6-00-000091: The system must ignore ICMPv4 redirect messages by default.
The status of the "net.ipv4.conf.default.accept_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.default.accept_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.default.accept_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
Fix
To set the runtime status of the "net.ipv4.conf.default.accept_redirects" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.default.accept_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.default.accept_redirects = 0
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208859r603263_rule'
OL6-00-000064: The system must use a FIPS 140-2 approved cryptographic hashing algorithm for generating account password hashes (libuser.conf).
Inspect "/etc/libuser.conf" and ensure the following line appears in the "[default]" section: crypt_style = sha512 If it does not, this is a finding.
Discussion
Using a stronger hashing algorithm makes password cracking attacks more difficult.
Fix
In "/etc/libuser.conf", add or correct the following line in its "[defaults]" section to ensure the system will use the SHA-512 algorithm for password hashing: crypt_style = sha512
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208839r603263_rule'
OL6-00-000005: The audit system must alert designated staff members when the audit storage volume approaches capacity.
Inspect '/etc/audit/auditd.conf' and locate the following line to determine if the system is configured to email the administrator when disk space is starting to run low: # grep space_left_action /etc/audit/auditd.conf space_left_action = email If the system is not configured to send an email to the system administrator when disk space is starting to run low, this is a finding. The 'syslog' option is acceptable when it can be demonstrated that the local log management infrastructure notifies an appropriate administrator in a timely manner.
Discussion
Notifying administrators of an impending disk space problem may allow them to take corrective action prior to any disruption.
Fix
The 'auditd' service can be configured to take an action when disk space starts to run low. Edit the file '/etc/audit/auditd.conf'. Modify the following line, substituting [ACTION] appropriately: space_left_action = [ACTION] Possible values for [ACTION] are described in the 'auditd.conf' man page. These include: 'ignore', 'syslog', 'email', 'exec', 'suspend', 'single', and 'halt'. Set this to 'email' (instead of the default, which is 'suspend') as it is more likely to get prompt attention. The 'syslog' option is acceptable, provided the local log management infrastructure notifies an appropriate administrator in a timely manner. OL6-00-000521 ensures that the email generated through the operation "space_left_action" will be sent to an administrator.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219542r603263_rule'
OL6-00-000246: The avahi service must be disabled.
To check that the "avahi-daemon" service is disabled in system boot configuration, run the following command: # chkconfig "avahi-daemon" --list Output should indicate the "avahi-daemon" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "avahi-daemon" --list "avahi-daemon" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "avahi-daemon" is disabled through current runtime configuration: # service avahi-daemon status If the service is disabled the command will return the following output: avahi-daemon is stopped If the service is running, this is a finding.
Discussion
Because the Avahi daemon service keeps an open network port, it is subject to network attacks. Its functionality is convenient but is only appropriate if the local network can be trusted.
Fix
The "avahi-daemon" service can be disabled with the following commands: # chkconfig avahi-daemon off # service avahi-daemon stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208929r603263_rule'
OL6-00-000292: The DHCP client must be disabled if not needed.
To verify that DHCP is not being used, examine the following file for each interface. # /etc/sysconfig/network-scripts/ifcfg-[IFACE] If there is any network interface without a associated "ifcfg" file, this is a finding. Look for the following: BOOTPROTO=none Also verify the following, substituting the appropriate values based on your site's addressing scheme: NETMASK=[local LAN netmask] IPADDR=[assigned IP address] GATEWAY=[local LAN default gateway] If it does not, this is a finding.
Discussion
DHCP relies on trusting the local network. If the local network is not trusted, then it should not be used. However, the automatic configuration provided by DHCP is commonly used and the alternative, manual configuration, presents an unacceptable burden in many circumstances.
Fix
For each interface [IFACE] on the system (e.g. eth0), edit "/etc/sysconfig/network-scripts/ifcfg-[IFACE]" and make the following changes. Correct the BOOTPROTO line to read: BOOTPROTO=none Add or correct the following lines, substituting the appropriate values based on your site's addressing scheme: NETMASK=[local LAN netmask] IPADDR=[assigned IP address] GATEWAY=[local LAN default gateway]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209024r603263_rule'
OL6-00-000045: Library files must have mode 0755 or less permissive.
System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: /lib /lib64 /usr/lib /usr/lib64 Kernel modules, which can be added to the kernel during runtime, are stored in "/lib/modules". All files in these directories should not be group-writable or world-writable. To find shared libraries that are group-writable or world-writable, run the following command for each directory [DIR] which contains shared libraries: $ find -L [DIR] -perm /022 -type f If any of these files (excluding broken symlinks) are group-writable or world-writable, this is a finding.
Discussion
Files from shared library directories are loaded into the address space of processes (including privileged ones) or of the kernel itself at runtime. Restrictive permissions are necessary to protect the integrity of the system.
Fix
System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: /lib /lib64 /usr/lib /usr/lib64 If any file in these directories is found to be group-writable or world-writable, correct its permission with the following command: # chmod go-w [FILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208822r603263_rule'
OL6-00-000040: The /etc/passwd file must be group-owned by root.
To check the group ownership of "/etc/passwd", run the command: $ ls -l /etc/passwd If properly configured, the output should indicate the following group-owner. "root" If it does not, this is a finding.
Discussion
The "/etc/passwd" file contains information about the users that are configured on the system. Protection of this file is critical for system security.
Fix
To properly set the group owner of "/etc/passwd", run the command: # chgrp root /etc/passwd
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208817r603263_rule'
OL6-00-000508: The system must allow locking of graphical desktop sessions.
If the GConf2 package is not installed, this is not applicable. Verify the keybindings for the Gnome screensaver: # gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gnome_settings_daemon/keybindings/screensaver If no output is visible, this is a finding.
Discussion
The ability to lock graphical desktop sessions manually allows users to easily secure their accounts should they need to depart from their workstations temporarily.
Fix
Run the following command to set the Gnome desktop keybinding for locking the screen: # gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type string \ --set /apps/gnome_settings_daemon/keybindings/screensaver "<Control><Alt>l" Another keyboard sequence may be substituted for "<Control><Alt>l", which is the default for the Gnome desktop.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209057r603263_rule'
OL6-00-000349: The system must be configured to require the use of a CAC, PIV compliant hardware token, or Alternate Logon Token (ALT) for authentication.
Interview the SA to determine if all accounts not exempted by policy are using CAC authentication. For DoD systems, the following systems and accounts are exempt from using smart card (CAC) authentication: Standalone systems Application accounts Temporary employee accounts, such as students or interns, who cannot easily receive a CAC or PIV Operational tactical locations that are not collocated with RAPIDS workstations to issue CAC or ALT Test systems, such as those with an Interim Approval to Test (IATT) and use a separate VPN, firewall, or security measure preventing access to network and system components from outside the protection boundary documented in the IATT. If non-exempt accounts are not using CAC authentication, this is a finding.
Discussion
Smart card login provides two-factor authentication stronger than that provided by a username/password combination. Smart cards leverage a PKI (public key infrastructure) in order to provide and verify credentials.
Fix
To enable smart card authentication, consult the documentation at: https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Managing_Smart_Cards/enabling-smart-card-login.html For guidance on enabling SSH to authenticate against a Common Access Card (CAC), consult documentation at: https://access.redhat.com/solutions/82273
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209051r603263_rule'
OL6-00-000195: The audit system must be configured to audit all discretionary access control permission modifications using removexattr.
To determine if the system is configured to audit calls to the "removexattr" system call, run the following command: $ sudo grep -w "removexattr" /etc/audit/audit.rules -a always,exit -F arch=b32 -S removexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S removexattr -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S removexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S removexattr -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "removexattr" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S removexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S removexattr -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S removexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S removexattr -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208904r603263_rule'
OL6-00-000518: The system package management tool must verify permissions on all files and directories associated with packages.
The following command will list which files and directories on the system have permissions different from what is expected by the RPM database: # rpm -Va | grep '^.M' If there is any output, for each file or directory found, find the associated RPM package and compare the RPM-expected permissions with the actual permissions on the file or directory: # rpm -qf [file or directory name] # rpm -q --queryformat "[%{FILENAMES} %{FILEMODES:perms}\n]" [package] | grep [filename] # ls -dlL [filename] If the existing permissions are more permissive than those expected by RPM, this is a finding.
Discussion
Permissions on system binaries and configuration files that are too generous could allow an unauthorized user to gain privileges that they should not have. The permissions set by the vendor should be maintained. Any deviations from this baseline should be investigated.
Fix
The RPM package management system can restore file access permissions of package files and directories. The following command will update permissions on files and directories with permissions different from what is expected by the RPM database: # rpm --setperms [package]
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209063r603263_rule'
OL6-00-000066: The system boot loader configuration file(s) must be group-owned by root.
To check the group ownership of "/boot/grub/grub.conf", run the command: $ ls -lL /boot/grub/grub.conf If properly configured, the output should indicate the group-owner is "root". If it does not, this is a finding.
Discussion
The "root" group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway.
Fix
The file "/boot/grub/grub.conf" should be group-owned by the "root" group to prevent destruction or modification of the file. To properly set the group owner of "/boot/grub/grub.conf", run the command: # chgrp root /boot/grub/grub.conf
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208841r603263_rule'
OL6-00-000319: The system must limit users to 10 simultaneous system logins, or a site-defined number, in accordance with operational requirements.
Run the following command to ensure the "maxlogins" value is configured for all users on the system: $ grep "maxlogins" /etc/security/limits.conf /etc/security/limits.d/*.conf You should receive output similar to the following: * hard maxlogins 10 If it is not similar, this is a finding.
Discussion
Limiting simultaneous user logins can insulate the system from denial of service problems caused by excessive logins. Automated login processes operating improperly or maliciously may result in an exceptional number of simultaneous login sessions.
Fix
Limiting the number of allowed users and sessions per user can limit risks related to denial of service attacks. This addresses concurrent sessions for a single account and does not address concurrent sessions by a single user via multiple accounts. To set the number of concurrent sessions per user add the following line in "/etc/security/limits.conf": * hard maxlogins 10 A documented site-defined number may be substituted for 10 in the above.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209033r603263_rule'
OL6-00-000010: The Oracle Linux operating system must be a vendor-supported release.
Verify the version of the operating system is vendor supported. Check the version of the operating system with the following command: # cat /etc/oracle-release Oracle Linux release 6.10 Current end of Support for Oracle Linux 6 is 31 March 2024. If the release is not supported by the vendor, this is a finding.
Discussion
An operating system release is considered "supported" if the vendor continues to provide security patches for the product. With an unsupported release, it will not be possible to resolve security issues discovered in the system software.
Fix
Upgrade to a supported version of the operating system.
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-224675r603263_rule'
OL6-00-000044: The /etc/group file must have mode 0644 or less permissive.
To check the permissions of "/etc/group", run the command: $ ls -l /etc/group If properly configured, the output should indicate the following permissions: "-rw-r--r--" If it does not, this is a finding.
Discussion
The "/etc/group" file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
Fix
To properly set the permissions of "/etc/group", run the command: # chmod 644 /etc/group
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208821r603263_rule'
OL6-00-000221: The ypbind service must not be running.
To check that the "ypbind" service is disabled in system boot configuration, run the following command: # chkconfig "ypbind" --list Output should indicate the "ypbind" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "ypbind" --list "ypbind" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "ypbind" is disabled through current runtime configuration: # service ypbind status If the service is disabled the command will return the following output: ypbind is stopped If the service is running, this is a finding.
Discussion
Disabling the "ypbind" service ensures the system is not acting as a client in a NIS or NIS+ domain.
Fix
The "ypbind" service, which allows the system to act as a client in a NIS or NIS+ domain, should be disabled. The "ypbind" service can be disabled with the following commands: # chkconfig ypbind off # service ypbind stop
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208918r603263_rule'
OL6-00-000344: The system default umask in /etc/profile must be 077.
Verify the "umask" setting is configured correctly in the "/etc/profile" file by running the following command: # grep "umask" /etc/profile All output must show the value of "umask" set to 077, as shown in the below: # grep "umask" /etc/profile umask 077 If the above command returns no output, or if the umask is configured incorrectly, this is a finding.
Discussion
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and/or written to by unauthorized users.
Fix
To ensure the default umask controlled by "/etc/profile" is set properly, add or correct the "umask" setting in "/etc/profile" to read as follows: umask 077
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209046r603263_rule'
OL6-00-000524: The system must provide automated support for account management functions.
Interview the SA to determine if there is an automated system for managing user accounts, preferably integrated with an existing enterprise user management system. If there is not, this is a finding.
Discussion
A comprehensive account management process that includes automation helps to ensure the accounts designated as requiring attention are consistently and promptly addressed. Enterprise environments make user account management challenging and complex. A user management process requiring administrators to manually address account management functions adds risk of potential oversight.
Fix
Implement an automated system for managing user accounts that minimizes the risk of errors, either intentional or deliberate. If possible, this system should integrate with an existing enterprise user management system, such as, one based Active Directory or Kerberos.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209067r603263_rule'
OL6-00-000230: The SSH daemon must set a timeout interval on idle sessions.
Run the following command to see what the timeout interval is: # grep ClientAliveInterval /etc/ssh/sshd_config ClientAliveInterval 600 If "ClientAliveInterval" has a value greater than "600", this is a finding.
Discussion
Causing idle users to be automatically logged out guards against compromises one system leading trivially to compromises on another.
Fix
SSH allows administrators to set an idle timeout interval. After this interval has passed, the idle user will be automatically logged out. To set an idle timeout interval, edit the following line in "/etc/ssh/sshd_config" as follows: ClientAliveInterval [interval] The timeout [interval] is given in seconds. To have a timeout of ten minutes, set [interval] to 600. If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made here. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208921r603340_rule'
OL6-00-000187: The audit system must be configured to audit all discretionary access control permission modifications using fchmodat.
To determine if the system is configured to audit calls to the "fchmodat" system call, run the following command: $ sudo grep -w "fchmodat" /etc/audit/audit.rules -a always,exit -F arch=b32 -S fchmodat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchmodat -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S fchmodat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchmodat -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "fchmodat" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S fchmodat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchmodat -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S fchmodat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchmodat -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208896r603263_rule'
OL6-00-000183: The audit system must be configured to audit modifications to the systems Mandatory Access Control (MAC) configuration (SELinux).
To determine if the system is configured to audit changes to its SELinux configuration files, run the following command: $ sudo grep -w "/etc/selinux" /etc/audit/audit.rules If the system is configured to watch for changes to its SELinux configuration, a line should be returned (including "-p wa" indicating permissions that are watched). If the system is not configured to audit attempts to change the MAC policy, this is a finding.
Discussion
The system's mandatory access policy (SELinux) should not be arbitrarily changed by anything other than administrator action. All changes to MAC policy should be audited.
Fix
Add the following to "/etc/audit/audit.rules": -w /etc/selinux/ -p wa -k MAC-policy
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208892r603263_rule'
OL6-00-000517: The system package management tool must verify group-ownership on all files and directories associated with packages.
The following command will list which files on the system have group-ownership different from what is expected by the RPM database: # rpm -Va | grep '^......G' If any output is produced, verify that the changes were due to STIG application and have been documented with the ISSO. If any output has not been documented with the ISSO, this is a finding.
Discussion
Group-ownership of system binaries and configuration files that is incorrect could allow an unauthorized user to gain privileges that they should not have. The group-ownership set by the vendor should be maintained. Any deviations from this baseline should be investigated.
Fix
The RPM package management system can restore group-ownership of the package files and directories. The following command will update files and directories with group-ownership different from what is expected by the RPM database: # rpm -qf [file or directory name] # rpm --setugids [package]
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209062r603263_rule'
OL6-00-000276: The operating system must protect the confidentiality and integrity of data at rest.
Determine if encryption must be used to protect data on the system. If encryption must be used and is not employed, this is a finding.
Discussion
The risk of a system's physical compromise, particularly mobile systems such as laptops, places its data at risk of compromise. Encrypting this data mitigates the risk of its loss if the system is lost.
Fix
The operating system natively supports partition encryption through the Linux Unified Key Setup (LUKS) on-disk-format technology. The easiest way to encrypt a partition is during installation time. For manual installations, select the "Encrypt" checkbox during partition creation to encrypt the partition. When this option is selected, the system will prompt for a passphrase to use in decrypting the partition. The passphrase will subsequently need to be entered manually every time the system boots. For automated/unattended installations, it is possible to use Kickstart by adding the "--encrypted" and "--passphrase=" options to the definition of each partition to be encrypted. For example, the following line would encrypt the root partition: part / --fstype=ext3 --size=100 --onpart=hda1 --encrypted --passphrase=[PASSPHRASE] Any [PASSPHRASE] is stored in the Kickstart in plaintext, and the Kickstart must then be protected accordingly. Omitting the "--passphrase=" option from the partition definition will cause the installer to pause and interactively ask for the passphrase during installation. Detailed information on encrypting partitions using LUKS can be found in the Oracle Linux documentation at: http://docs.oracle.com/cd/E37670_01/E36387/html/index.html Additional information is available from: http://linux.oracle.com/documentation/OL6/Red_Hat_Enterprise_Linux-6-Security_Guide-en-US.pdf
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209013r603263_rule'
OL6-00-000286: The x86 Ctrl-Alt-Delete key sequence must be disabled.
To ensure the system is configured to log a message instead of rebooting the system when “Ctrl-Alt-Delete” is pressed, ensure the following line is in "/etc/init/control-alt-delete.override": exec /usr/bin/logger -p authpriv.notice "Ctrl-Alt-Delete pressed" If the system is not configured to block the shutdown command when “Ctrl-Alt-Delete” is pressed, this is a finding.
Discussion
A locally logged-on user who presses Ctrl-Alt-Delete, when at the console, can reboot the system. If accidentally pressed, as could happen in the case of mixed OS environment, this can create the risk of short-term loss of availability of systems due to unintentional reboot. In the GNOME graphical environment, risk of unintentional reboot from the Ctrl-Alt-Delete sequence is reduced because the user will be prompted before any action is taken.
Fix
By default, the system includes the following line in "/etc/init/control-alt-delete.conf" to reboot the system when the “Ctrl-Alt-Delete” key sequence is pressed: exec /sbin/shutdown -r now "Ctrl-Alt-Delete pressed" To configure the system to log a message instead of rebooting the system, add the following line to "/etc/init/control-alt-delete.override" to read as follows: exec /usr/bin/logger -p authpriv.notice "Ctrl-Alt-Delete pressed"
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-209019r603263_rule'
OL6-00-000038: The /etc/gshadow file must have mode 0000.
To check the permissions of "/etc/gshadow", run the command: $ ls -l /etc/gshadow If properly configured, the output should indicate the following permissions: "----------" If it does not, this is a finding.
Discussion
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.
Fix
To properly set the permissions of "/etc/gshadow", run the command: # chmod 0000 /etc/gshadow
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208815r603263_rule'
OL6-00-000182: The audit system must be configured to audit modifications to the systems network configuration.
If you are running x86_64 architecture, determine the values for sethostname: $ uname -m; ausyscall i386 sethostname; ausyscall x86_64 sethostname If the values returned are not identical verify that the system is configured to monitor network configuration changes for the i386 and x86_64 architectures: $ sudo egrep -w '(sethostname|setdomainname|/etc/issue|/etc/issue.net|/etc/hosts|/etc/sysconfig/network)' /etc/audit/audit.rules -a always,exit -F arch=b32 -S sethostname -S setdomainname -k audit_network_modifications -w /etc/issue -p wa -k audit_network_modifications -w /etc/issue.net -p wa -k audit_network_modifications -w /etc/hosts -p wa -k audit_network_modifications -w /etc/sysconfig/network -p wa -k audit_network_modifications -a always,exit -F arch=b64 -S sethostname -S setdomainname -k audit_network_modifications -w /etc/issue -p wa -k audit_network_modifications -w /etc/issue.net -p wa -k audit_network_modifications -w /etc/hosts -p wa -k audit_network_modifications -w /etc/sysconfig/network -p wa -k audit_network_modifications If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit changes of the network configuration, this is a finding.
Discussion
The network environment should not be modified by anything other than administrator action. Any change to network parameters should be audited.
Fix
Add the following to "/etc/audit/audit.rules": # audit_network_modifications -a always,exit -F arch=b32 -S sethostname -S setdomainname -k audit_network_modifications -w /etc/issue -p wa -k audit_network_modifications -w /etc/issue.net -p wa -k audit_network_modifications -w /etc/hosts -p wa -k audit_network_modifications -w /etc/sysconfig/network -p wa -k audit_network_modifications If the system is 64-bit, then also add the following: # audit_network_modifications -a always,exit -F arch=b64 -S sethostname -S setdomainname -k audit_network_modifications
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208891r603263_rule'
OL6-00-000503: The operating system must enforce requirements for the connection of mobile devices to operating systems.
If the system is configured to prevent the loading of the "usb-storage" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": $ grep -r usb-storage /etc/modprobe.conf /etc/modprobe.d | grep -i “/bin/true” If no line is returned, this is a finding.
Discussion
USB storage devices such as thumb drives can be used to introduce unauthorized software and other vulnerabilities. Support for these devices should be disabled and the devices themselves should be tightly controlled.
Fix
To prevent USB storage devices from being used, configure the kernel module loading system to prevent automatic loading of the USB storage driver. To configure the system to prevent the "usb-storage" kernel module from being loaded, add the following line to a file in the directory "/etc/modprobe.d": install usb-storage /bin/true This will prevent the "modprobe" program from loading the "usb-storage" module, but will not prevent an administrator (or another program) from using the "insmod" program to load the module manually.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219584r603263_rule'
OL6-00-000092: The system must not respond to ICMPv4 sent to a broadcast address.
The status of the "net.ipv4.icmp_echo_ignore_broadcasts" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.icmp_echo_ignore_broadcasts The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.
Fix
To set the runtime status of the "net.ipv4.icmp_echo_ignore_broadcasts" kernel parameter, run the following command: # sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.icmp_echo_ignore_broadcasts = 1
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208860r603263_rule'
OL6-00-000050: The system must require passwords to contain a minimum of 15 characters.
To check the minimum password length, run the command: $ grep PASS_MIN_LEN /etc/login.defs The DoD requirement is "15". If it is not set to the required value, this is a finding. $ grep –E ‘pam_cracklib.so.*minlen’ /etc/pam.d/* If no results are returned, this is not a finding. If any results are returned and are not set to “15” or greater, this is a finding.
Discussion
Requiring a minimum password length makes password cracking attacks more difficult by ensuring a larger search space. However, any security benefit from an onerous requirement must be carefully weighed against usability problems, support costs, or counterproductive behavior that may result. While it does not negate the password length requirement, it is preferable to migrate from a password-based authentication scheme to a stronger one based on PKI (public key infrastructure).
Fix
To specify password length requirements for new accounts, edit the file "/etc/login.defs" and add or correct the following lines: PASS_MIN_LEN 15 The DoD requirement is "15". If a program consults "/etc/login.defs" and also another PAM module (such as "pam_cracklib") during a password change operation, then the most restrictive must be satisfied.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208826r603263_rule'
OL6-00-000252: If the system is using LDAP for authentication or account information, the system must use a TLS connection using FIPS 140-2 approved cryptographic algorithms.
If the system does not use LDAP for authentication or account information, this is not applicable. To ensure LDAP is configured to use TLS for all transactions, run the following command: $ grep start_tls /etc/pam_ldap.conf If no lines are returned, this is a finding.
Discussion
The ssl directive specifies whether to use ssl or not. If not specified it will default to "no". It should be set to "start_tls" rather than doing LDAP over SSL.
Fix
Configure LDAP to enforce TLS use. First, edit the file "/etc/pam_ldap.conf", and add or correct the following lines: ssl start_tls Then review the LDAP server and ensure TLS has been configured.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208931r603263_rule'
OL6-00-000161: The system must rotate audit log files that reach the maximum file size.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine if the system is configured to rotate logs when they reach their maximum size: # grep max_log_file_action /etc/audit/auditd.conf max_log_file_action = rotate If the "keep_logs" option is configured for the "max_log_file_action" line in "/etc/audit/auditd.conf" and an alternate process is in place to ensure audit data does not overwhelm local audit storage, this is not a finding. If the system has not been properly set up to rotate audit logs, this is a finding.
Discussion
Automatically rotating logs (by setting this to "rotate") minimizes the chances of the system unexpectedly running out of disk space by being overwhelmed with log data. However, for systems that must never discard log data, or which use external processes to transfer it and reclaim space, "keep_logs" can be employed.
Fix
The default action to take when the logs reach their maximum size is to rotate the log files, discarding the oldest one. To configure the action taken by "auditd", add or correct the line in "/etc/audit/auditd.conf": max_log_file_action = [ACTION] Possible values for [ACTION] are described in the "auditd.conf" man page. These include: "ignore" "syslog" "suspend" "rotate" "keep_logs" Set the "[ACTION]" to "rotate" to ensure log rotation occurs. This is the default. The setting is case-insensitive.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208880r603263_rule'
OL6-00-000159: The system must retain enough rotated audit logs to cover the required log retention period.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine how many logs the system is configured to retain after rotation: "# grep num_logs /etc/audit/auditd.conf" num_logs = 5 If the overall system log file(s) retention hasn't been properly set up, this is a finding.
Discussion
The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.
Fix
Determine how many log files "auditd" should retain when it rotates logs. Edit the file "/etc/audit/auditd.conf". Add or modify the following line, substituting [NUMLOGS] with the correct value: num_logs = [NUMLOGS] Set the value to 5 for general-purpose systems. Note that values less than 2 result in no log rotation.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208878r603263_rule'
OL6-00-000090: The system must not accept ICMPv4 secure redirect packets by default.
The status of the "net.ipv4.conf.default.secure_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.default.secure_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.default.secure_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required.
Fix
To set the runtime status of the "net.ipv4.conf.default.secure_redirects" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.default.secure_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.default.secure_redirects = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208858r603263_rule'
OL6-00-000067: The system boot loader configuration file(s) must have mode 0600 or less permissive.
To check the permissions of "/boot/grub/grub.conf", run the command: $ sudo ls -lL /boot/grub/grub.conf If properly configured, the output should indicate the following permissions: "-rw-------" If it does not, this is a finding.
Discussion
Proper permissions ensure that only the root user can modify important boot parameters.
Fix
File permissions for "/boot/grub/grub.conf" should be set to 600, which is the default. To properly set the permissions of "/boot/grub/grub.conf", run the command: # chmod 600 /boot/grub/grub.conf Boot partitions based on VFAT, NTFS, or other non-standard configurations may require alternative measures.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208842r603263_rule'
OL6-00-000288: The sendmail package must be removed.
Run the following command to determine if the "sendmail" package is installed: # rpm -q sendmail If the package is installed, this is a finding.
Discussion
The sendmail software was not developed with security in mind and its design prevents it from being effectively contained by SELinux. Postfix should be used instead.
Fix
Sendmail is not the default mail transfer agent and is not installed by default. The "sendmail" package can be removed with the following command: # yum erase sendmail
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209021r603263_rule'
OL6-00-000313: The audit system must identify staff members to receive notifications of audit log storage volume capacity issues.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine if the system is configured to send email to an account when it needs to notify an administrator: action_mail_acct = root If auditd is not configured to send emails per identified actions, this is a finding.
Discussion
Email sent to the root account is typically aliased to the administrators of the system, who can take appropriate action.
Fix
The "auditd" service can be configured to send email to a designated account in certain situations. Add or correct the following line in "/etc/audit/auditd.conf" to ensure that administrators are notified via email for those situations: action_mail_acct = root
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209032r603263_rule'
OL6-00-000536: The Oracle Linux operating system must use the invoking user's password for privilege escalation when using "sudo".
Verify that the sudoers security policy is configured to use the invoking user's password for privilege escalation. $ sudo egrep -i '(!rootpw|!targetpw|!runaspw)' /etc/sudoers /etc/sudoers.d/* | grep -v '#' /etc/sudoers:Defaults !targetpw /etc/sudoers:Defaults !rootpw /etc/sudoers:Defaults !runaspw If no results are returned, this is a finding If "Defaults !targetpw" is not defined, this is a finding. If "Defaults !rootpw" is not defined, this is a finding. If "Defaults !runaspw" is not defined, this is a finding.
Discussion
The sudoers security policy requires that users authenticate themselves before they can use sudo. When sudoers requires authentication, it validates the invoking user's credentials. If the rootpw, targetpw, or runaspw flags are defined and not disabled, by default the operating system will prompt the invoking user for the "root" user password. For more information on each of the listed configurations, reference the sudoers(5) manual page.
Fix
Define the following in the Defaults section of the /etc/sudoers file or a configuration file in the /etc/sudoers.d/ directory: Defaults !targetpw Defaults !rootpw Defaults !runaspw
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-237625r646946_rule'
OL6-00-000200: The audit system must be configured to audit user deletions of files and programs.
To determine if the system is configured to audit user deletions of files and programs, run the following command: $ sudo egrep -w 'rmdir|unlink|unlinkat|rename|renameat' /etc/audit/audit.rules -a always,exit -F arch=b32 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete -a always,exit -F arch=b32 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid=0 -k delete -a always,exit -F arch=b64 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete -a always,exit -F arch=b64 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid=0 -k delete If the system is 64-bit and does not return rules for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit "rmdir", this is a finding. If the system is not configured to audit "unlink", this is a finding. If the system is not configured to audit "unlinkat", this is a finding. If the system is not configured to audit "rename", this is a finding. If the system is not configured to audit "renameat", this is a finding. If no line is returned, this is a finding.
Discussion
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as detecting malicious processes that attempt to delete log files to conceal their presence.
Fix
At a minimum, the audit system should collect file deletion events for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete -a always,exit -F arch=b32 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid=0 -k delete If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=500 -F auid!=4294967295 -k delete -a always,exit -F arch=b64 -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid=0 -k delete
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208908r603263_rule'
OL6-00-000116: The operating system must connect to external networks or information systems only through managed IPv4 interfaces consisting of boundary protection devices arranged in accordance with an organizational security architecture.
If the system is a cross-domain system, this is not applicable. Run the following command to determine the current status of the "iptables" service: # service iptables status If the service is not running, it should return the following: iptables: Firewall is not running. If the service is not running, this is a finding.
Discussion
The "iptables" service provides the system's host-based firewalling capability for IPv4 and ICMP.
Fix
The "iptables" service can be enabled with the following commands: # chkconfig iptables on # service iptables start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219552r603263_rule'
OL6-00-000202: The audit system must be configured to audit the loading and unloading of dynamic kernel modules.
To determine if the system is configured to audit execution of module management programs, run the following commands: sudo egrep -e "(-w |-F path=)/sbin/insmod|(-w |-F path=)/sbin/rmmod|(-w |-F path=)/sbin/modprobe" /etc/audit/audit.rules -w /sbin/insmod -p x -k modules -w /sbin/rmmod -p x -k modules -w /sbin/modprobe -p x -k modules If "/sbin/insmod" is not being audited, this is a finding. If "/sbin/rmmod" is not being audited, this is a finding. If "/sbin/modprobe" is not being audited, this is a finding. To determine if the system is configured to audit calls to the "init_module" and "delete_module" system calls, run the following command: $ sudo egrep -w "init_module|delete_module" /etc/audit/audit.rules -a always,exit -F arch=b32 -S init_module -S delete_module -k modules -a always,exit -F arch=b64 -S init_module -S delete_module -k modules If the system is 64-bit and does not return rules for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit "init_module" this is a finding. If the system is not configured to audit "delete_module", this is a finding. If no line is returned, this is a finding.
Discussion
The addition/removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel.
Fix
Add the following to "/etc/audit/audit.rules" in order to capture kernel module loading and unloading events: -w /sbin/insmod -p x -k modules -w /sbin/rmmod -p x -k modules -w /sbin/modprobe -p x -k modules -a always,exit -F arch=b32 -S init_module -S delete_module -k modules If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S init_module -S delete_module -k modules
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208910r603263_rule'
OL6-00-000259: The graphical desktop environment must have automatic lock enabled.
If the GConf2 package is not installed, this is not applicable. To check the status of the idle screen lock activation, run the following command: $ gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gnome-screensaver/lock_enabled If properly configured, the output should be "true". If it is not, this is a finding.
Discussion
Enabling the activation of the screen lock after an idle period ensures password entry will be required in order to access the system, preventing access by passersby.
Fix
Run the following command to activate locking of the screensaver in the GNOME desktop when it is activated: # gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type bool \ --set /apps/gnome-screensaver/lock_enabled true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208935r603263_rule'
OL6-00-000507: The operating system, upon successful logon, must display to the user the date and time of the last logon or access via ssh.
Verify the value associated with the "PrintLastLog" keyword in /etc/ssh/sshd_config: # grep -i "^PrintLastLog" /etc/ssh/sshd_config If the "PrintLastLog" keyword is not present, this is not a finding. If the value is not set to "yes", this is a finding.
Discussion
Users need to be aware of activity that occurs regarding their account. Providing users with information regarding the date and time of their last successful login allows the user to determine if any unauthorized activity has occurred and gives them an opportunity to notify administrators. At ssh login, a user must be presented with the last successful login date and time.
Fix
Update the "PrintLastLog" keyword to "yes" in /etc/ssh/sshd_config: PrintLastLog yes While it is acceptable to remove the keyword entirely since the default action for the SSH daemon is to print the last login date and time, it is preferred to have the value explicitly documented.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209056r603263_rule'
OL6-00-000346: The system default umask for daemons must be 027 or 022.
To check the value of the "umask", run the following command: $ grep umask /etc/init.d/functions The output should show either "022" or "027". If it does not, this is a finding.
Discussion
The umask influences the permissions assigned to files created by a process at run time. An unnecessarily permissive umask could result in files being created with insecure permissions.
Fix
The file "/etc/init.d/functions" includes initialization parameters for most or all daemons started at boot time. The default umask of 022 prevents creation of group- or world-writable files. To set the default umask for daemons, edit the following line, inserting 022 or 027 for [UMASK] appropriately: umask [UMASK] Setting the umask to too restrictive a setting can cause serious errors at runtime. Many daemons on the system already individually restrict themselves to a umask of 077 in their own init scripts.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209048r603263_rule'
OL6-00-000065: The system boot loader configuration file(s) must be owned by root.
To check the ownership of "/boot/grub/grub.conf", run the command: $ ls -lL /boot/grub/grub.conf If properly configured, the output should indicate that the owner is "root". If it does not, this is a finding.
Discussion
Only root should be able to modify important boot parameters.
Fix
The file "/boot/grub/grub.conf" should be owned by the "root" user to prevent destruction or modification of the file. To properly set the owner of "/boot/grub/grub.conf", run the command: # chown root /boot/grub/grub.conf
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208840r603263_rule'
OL6-00-000291: The xorg-x11-server-common (X Windows) package must not be installed, unless required.
To ensure the X Windows package group is removed, run the following command: $ rpm -qi xorg-x11-server-common The output should be: package xorg-x11-server-common is not installed If it is not, this is a finding.
Discussion
Unnecessary packages should not be installed to decrease the attack surface of the system.
Fix
Removing all packages which constitute the X Window System ensures users or malicious software cannot start X. To do so, run the following command: # yum groupremove "X Window System"
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209023r603263_rule'
OL6-00-000533: The Oracle Linux 6 operating system must use a virus scan program.
Verify an antivirus solution is installed on the system. The anti-virus solution may be bundled with an approved host-based security solution. If there is no antivirus solution installed on the system, this is a finding.
Discussion
Virus scanning software can be used to protect a system from penetration from computer viruses and to limit their spread through intermediate systems. The virus scanning software should be configured to perform scans dynamically on accessed files. If this capability is not available, the system must be configured to scan, at a minimum, all altered files on the system on a daily basis. If the system processes inbound SMTP mail, the virus scanner must be configured to scan all received mail.
Fix
Install an antivirus solution on the system.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219589r603263_rule'
OL6-00-000311: The audit system must provide a warning when allocated audit record storage volume reaches a documented percentage of maximum audit record storage capacity.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine whether the system is configured to email the administrator when disk space is starting to run low: # grep space_left /etc/audit/auditd.conf space_left = [num_megabytes] If the "num_megabytes" value does not correspond to a documented value for remaining audit partition capacity or if there is no locally documented value for remaining audit partition capacity, this is a finding.
Discussion
Notifying administrators of an impending disk space problem may allow them to take corrective action prior to any disruption.
Fix
The "auditd" service can be configured to take an action when disk space starts to run low. Edit the file "/etc/audit/auditd.conf". Modify the following line, substituting [num_megabytes] appropriately: space_left = [num_megabytes] The "num_megabytes" value should be set to a fraction of the total audit storage capacity available that will allow a system administrator to be notified with enough time to respond to the situation causing the capacity issues. This value must also be documented locally.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219577r603263_rule'
OL6-00-000201: The audit system must be configured to audit changes to the /etc/sudoers file.
To verify that auditing is configured for system administrator actions, run the following command: $ sudo grep -w "/etc/sudoers" /etc/audit/audit.rules If the system is configured to watch for changes to its sudoers configuration, a line should be returned (including "-p wa" indicating permissions that are watched). If there is no output, this is a finding.
Discussion
The actions taken by system administrators should be audited to keep a record of what was executed on the system, as well as, for accountability purposes.
Fix
At a minimum, the audit system should collect administrator actions for all users and root. Add the following to "/etc/audit/audit.rules": -w /etc/sudoers -p wa -k actions
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208909r603263_rule'
OL6-00-000262: The atd service must be disabled.
If the system requires the use of the "atd" service to support an organizational requirement, this is not applicable. To check that the "atd" service is disabled in system boot configuration, run the following command: # chkconfig "atd" --list Output should indicate the "atd" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "atd" --list "atd" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "atd" is disabled through current runtime configuration: # service atd status If the service is disabled the command will return the following output: atd is stopped If the service is running, this is a finding.
Discussion
The "atd" service could be used by an unsophisticated insider to carry out activities outside of a normal login session, which could complicate accountability. Furthermore, the need to schedule tasks with "at" or "batch" is not common.
Fix
The "at" and "batch" commands can be used to schedule tasks that are meant to be executed only once. This allows delayed execution in a manner similar to cron, except that it is not recurring. The daemon "atd" keeps track of tasks scheduled via "at" and "batch", and executes them at the specified time. The "atd" service can be disabled with the following commands: # chkconfig atd off # service atd stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208938r603263_rule'
OL6-00-000224: The cron service must be running.
Run the following command to determine the current status of the "crond" service: # service crond status If the service is enabled, it should return the following: crond is running... If the service is not running, this is a finding.
Discussion
Due to its usage for maintenance and security-supporting tasks, enabling the cron daemon is essential.
Fix
The "crond" service is used to execute commands at preconfigured times. It is required by almost all systems to perform necessary maintenance tasks, such as notifying root of system activity. The "crond" service can be enabled with the following commands: # chkconfig crond on # service crond start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208920r603263_rule'
OL6-00-000510: The audit system must take appropriate action when the audit storage volume is full.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine if the system is configured to take appropriate action when the audit storage volume is full: # grep disk_full_action /etc/audit/auditd.conf disk_full_action = [ACTION] If the system is configured to "suspend" when the volume is full or "ignore" that it is full, this is a finding.
Discussion
Taking appropriate action in case of a filled audit storage volume will minimize the possibility of losing audit records.
Fix
The "auditd" service can be configured to take an action when disk space starts to run low. Edit the file "/etc/audit/auditd.conf". Modify the following line, substituting [ACTION] appropriately: disk_full_action = [ACTION] Possible values for [ACTION] are described in the "auditd.conf" man page. These include: "ignore" "syslog" "exec" "suspend" "single" "halt" Set this to "syslog", "exec", "single", or "halt".
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209058r603263_rule'
OL6-00-000021: The Oracle Linux operating system must not contain .shosts or shosts.equiv files.
Verify there are no ".shosts" or "shosts.equiv" files on the system. # find / -name '*.shosts' # find / -name shosts.equiv If any ".shosts" or "shosts.equiv" files are found on the system, this is a finding.
Discussion
The .shosts and shosts.equiv files are used to configure host-based authentication for the system via SSH. Host-based authentication is not sufficient for preventing unauthorized access to the system, as it does not require interactive identification and authentication of a connection request, or for the use of two-factor authentication.
Fix
Remove any found ".shosts" or "shosts.equiv" files from the system. # rm /[path]/[to]/[file]/.shosts # rm /[path]/[to]/[file]/shosts.equiv
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-219957r603263_rule'
OL6-00-000222: The tftp-server package must not be installed unless required.
Run the following command to determine if the "tftp-server" package is installed: # rpm -q tftp-server If the package is installed and not documented and approved by the ISSO, this is a finding.
Discussion
Removing the "tftp-server" package decreases the risk of the accidental (or intentional) activation of tftp services.
Fix
The "tftp-server" package can be removed with the following command: # yum erase tftp-server
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208919r603263_rule'
OL6-00-000324: A login banner must be displayed immediately prior to, or as part of, graphical desktop environment login prompts.
If the GConf2 package is not installed, this is not applicable. To ensure a login warning banner is enabled, run the following: $ gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gdm/simple-greeter/banner_message_enable Search for the "banner_message_enable" schema. If properly configured, the "default" value should be "true". If it is not, this is a finding.
Discussion
An appropriate warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers.
Fix
To enable displaying a login warning banner in the GNOME Display Manager's login screen, run the following command: # gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type bool \ --set /apps/gdm/simple-greeter/banner_message_enable true To display a banner, this setting must be enabled and then banner text must also be set.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209034r603263_rule'
OL6-00-000356: The system must require administrator action to unlock an account locked by excessive failed login attempts.
To ensure the failed password attempt policy is configured correctly, run the following command: # grep pam_faillock /etc/pam.d/system-auth /etc/pam.d/password-auth If the "unlock_time" parameter is set to a value other than "0", "never", or less than "900" on "auth" lines with the "pam_faillock.so" module, or is missing from these lines, this is a finding. Note: The maximum configurable value for "unlock_time" is "604800".
Discussion
Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks. Ensuring that an administrator is involved in unlocking locked accounts draws appropriate attention to such situations.
Fix
To configure the system to lock out accounts after a number of incorrect logon attempts and require an administrator to unlock the account using "pam_faillock.so", modify the content of both "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" as follows: Add the following line immediately before the "pam_unix.so" statement in the "AUTH" section: auth required pam_faillock.so preauth silent deny=3 unlock_time=900 fail_interval=900 Add the following line immediately after the "pam_unix.so" statement in the "AUTH" section: auth [default=die] pam_faillock.so authfail deny=3 unlock_time=900 fail_interval=900 Add the following line immediately before the "pam_unix.so" statement in the "ACCOUNT" section: account required pam_faillock.so Note that any updates made to "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" may be overwritten by the "authconfig" program. The "authconfig" program should not be used.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219582r603263_rule'
OL6-00-000089: The system must not accept IPv4 source-routed packets by default.
The status of the "net.ipv4.conf.default.accept_source_route" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.default.accept_source_route The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.default.accept_source_route /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
Fix
To set the runtime status of the "net.ipv4.conf.default.accept_source_route" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.default.accept_source_route=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.default.accept_source_route = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208857r603263_rule'
OL6-00-000004: The system must use a separate file system for the system audit data path.
Run the following command to determine if "/var/log/audit" is on its own partition or logical volume: $ mount | grep "on /var/log/audit " If "/var/log/audit" has its own partition or volume group, a line will be returned. If no line is returned, this is a finding.
Discussion
Placing "/var/log/audit" in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.
Fix
Audit logs are stored in the "/var/log/audit" directory. Ensure that it has its own partition or logical volume at installation time, or migrate it later using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219541r603263_rule'
OL6-00-000345: The system default umask in /etc/login.defs must be 077.
Verify the "umask" setting is configured correctly in the "/etc/login.defs" file by running the following command: # grep -i "umask" /etc/login.defs All output must show the value of "umask" set to 077, as shown in the below: # grep -i "umask" /etc/login.defs UMASK 077 If the above command returns no output, or if the umask is configured incorrectly, this is a finding.
Discussion
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and/or written to by unauthorized users.
Fix
To ensure the default umask controlled by "/etc/login.defs" is set properly, add or correct the "umask" setting in "/etc/login.defs" to read as follows: UMASK 077
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209047r603263_rule'
OL6-00-000020: The system must use a Linux Security Module configured to enforce limits on system services.
Check the file "/etc/selinux/config" and ensure the following line appears: SELINUX=enforcing If SELINUX is not set to enforcing, this is a finding.
Discussion
Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.
Fix
The SELinux state should be set to "enforcing" at system boot time. In the file "/etc/selinux/config", add or correct the following line to configure the system to boot into enforcing mode: SELINUX=enforcing
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208801r603263_rule'
OL6-00-000016: A file integrity tool must be installed.
If another file integrity tool is installed, this is not a finding. Run the following command to determine if the "aide" package is installed: # rpm -q aide If the package is not installed, this is a finding.
Discussion
The AIDE package must be installed if it is to be available for integrity checking.
Fix
Install the AIDE package with the command: # yum install aide
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219546r603263_rule'
OL6-00-000253: The LDAP client must use a TLS connection using trust certificates signed by the site CA.
If the system does not use LDAP for authentication or account information, this is not applicable. To ensure TLS is configured with trust certificates, run the following command: # grep cert /etc/pam_ldap.conf If there is no output, or the lines are commented out, this is a finding.
Discussion
The tls_cacertdir or tls_cacertfile directives are required when tls_checkpeer is configured (which is the default for openldap versions 2.1 and up). These directives define the path to the trust certificates signed by the site CA.
Fix
Ensure a copy of the site's CA certificate has been placed in the file "/etc/pki/tls/CA/cacert.pem". Configure LDAP to enforce TLS use and to trust certificates signed by the site's CA. First, edit the file "/etc/pam_ldap.conf", and add or correct either of the following lines: tls_cacertdir /etc/pki/tls/CA or tls_cacertfile /etc/pki/tls/CA/cacert.pem Then review the LDAP server and ensure TLS has been configured.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219564r603263_rule'
OL6-00-000261: The Automatic Bug Reporting Tool (abrtd) service must not be running.
To check that the "abrtd" service is disabled in system boot configuration, run the following command: # chkconfig "abrtd" --list Output should indicate the "abrtd" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "abrtd" --list "abrtd" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "abrtd" is disabled through current runtime configuration: # service abrtd status If the service is disabled the command will return the following output: abrtd is stopped If the service is running, this is a finding.
Discussion
Mishandling crash data could expose sensitive information about vulnerabilities in software executing on the local machine, as well as sensitive information from within a process's address space or registers.
Fix
The Automatic Bug Reporting Tool ("abrtd") daemon collects and reports crash data when an application crash is detected. Using a variety of plugins, abrtd can email crash reports to system administrators, log crash reports to files, or forward crash reports to a centralized issue-tracking system such as the operating system vendor's centralized issue-tracking system. The "abrtd" service can be disabled with the following commands: # chkconfig abrtd off # service abrtd stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208937r603263_rule'
OL6-00-000127: The Transparent Inter-Process Communication (TIPC) protocol must be disabled unless required.
If the system is configured to prevent the loading of the "tipc" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": $ grep -r tipc /etc/modprobe.conf /etc/modprobe.d | grep -i “/bin/true” If no line is returned, this is a finding.
Discussion
Disabling TIPC protects the system against exploitation of any flaws in its implementation.
Fix
The Transparent Inter-Process Communication (TIPC) protocol is designed to provide communications between nodes in a cluster. To configure the system to prevent the "tipc" kernel module from being loaded, add the following line to a file in the directory "/etc/modprobe.d": install tipc /bin/true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208869r603263_rule'
OL6-00-000267: The qpidd service must not be running.
To check that the "qpidd" service is disabled in system boot configuration, run the following command: # chkconfig "qpidd" --list Output should indicate the "qpidd" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "qpidd" --list "qpidd" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "qpidd" is disabled through current runtime configuration: # service qpidd status If the service is disabled the command will return the following output: qpidd is stopped If the service is running, this is a finding.
Discussion
The qpidd service is automatically installed when the "base" package selection is selected during installation. The qpidd service listens for network connections, which increases the attack surface of the system. If the system is not intended to receive AMQP, traffic then the "qpidd" service is not needed and should be disabled or removed.
Fix
The "qpidd" service provides high speed, secure, guaranteed delivery services. It is an implementation of the Advanced Message Queuing Protocol. By default the qpidd service will bind to port 5672 and listen for connection attempts. The "qpidd" service can be disabled with the following commands: # chkconfig qpidd off # service qpidd stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208941r603263_rule'
OL6-00-000535: The Oracle Linux operating system must restrict privilege elevation to authorized personnel.
Verify the "sudoers" file restricts sudo access to authorized personnel. $ sudo grep -iw 'ALL' /etc/sudoers /etc/sudoers.d/* If the either of the following entries are returned, this is a finding: ALL ALL=(ALL) ALL ALL ALL=(ALL:ALL) ALL
Discussion
The sudo command allows a user to execute programs with elevated (administrator) privileges. It prompts the user for their password and confirms your request to execute a command by checking a file, called sudoers. If the "sudoers" file is not configured correctly, any user defined on the system can initiate privileged actions on the target system.
Fix
Remove the following entries from the sudoers file: ALL ALL=(ALL) ALL ALL ALL=(ALL:ALL) ALL
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-237624r646943_rule'
OL6-00-000231: The SSH daemon must set a timeout count on idle sessions.
To ensure the SSH idle timeout will occur when the "ClientAliveCountMax" is set, run the following command: # grep ClientAliveCountMax /etc/ssh/sshd_config If properly configured, output should be: ClientAliveCountMax 0 If it is not, this is a finding.
Discussion
This ensures a user login will be terminated as soon as the "ClientAliveCountMax" is reached.
Fix
To ensure the SSH idle timeout occurs precisely when the "ClientAliveCountMax" is set, edit "/etc/ssh/sshd_config" as follows: ClientAliveCountMax 0
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208922r603263_rule'
OL6-00-000041: The /etc/passwd file must have mode 0644 or less permissive.
To check the permissions of "/etc/passwd", run the command: $ ls -l /etc/passwd If properly configured, the output should indicate the following permissions: "-rw-r--r--" If it does not, this is a finding.
Discussion
If the "/etc/passwd" file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security.
Fix
To properly set the permissions of "/etc/passwd", run the command: # chmod 0644 /etc/passwd
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208818r603263_rule'
OL6-00-000042: The /etc/group file must be owned by root.
To check the ownership of "/etc/group", run the command: $ ls -l /etc/group If properly configured, the output should indicate the following owner: "root" If it does not, this is a finding.
Discussion
The "/etc/group" file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
Fix
To properly set the owner of "/etc/group", run the command: # chown root /etc/group
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208819r603263_rule'
OL6-00-000522: Audit log files must be group-owned by root.
Run the following command to check the group owner of the system audit logs: grep "^log_file" /etc/audit/auditd.conf|sed s/^[^\/]*//|xargs stat -c %G:%n Audit logs must be group-owned by root. If they are not, this is a finding.
Discussion
If non-privileged users can write to audit logs, audit trails can be modified or destroyed.
Fix
Change the group owner of the audit log files with the following command: # chgrp root [audit_file]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209066r603263_rule'
OL6-00-000086: The system must not accept ICMPv4 secure redirect packets on any interface.
The status of the "net.ipv4.conf.all.secure_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.secure_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.all.secure_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required.
Fix
To set the runtime status of the "net.ipv4.conf.all.secure_redirects" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.secure_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.secure_redirects = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208855r603263_rule'
OL6-00-000199: The audit system must be configured to audit successful file system mounts.
To verify that auditing is configured for all media exportation events, run the following command: $ sudo grep -w "mount" /etc/audit/audit.rules -a always,exit -F arch=b32 -S mount -F auid>=500 -F auid!=4294967295 -k export -a always,exit -F arch=b32 -S mount -F auid=0 -k export -a always,exit -F arch=b64 -S mount -F auid>=500 -F auid!=4294967295 -k export -a always,exit -F arch=b64 -S mount -F auid=0 -k export If the system is 64-bit and does not return rules for both "b32" and "b64" architectures, this is a finding. If no line is returned, this is a finding.
Discussion
The unauthorized exportation of data to external media could result in an information leak where classified information, Privacy Act information, and intellectual property could be lost. An audit trail should be created each time a filesystem is mounted to help identify and guard against information loss.
Fix
At a minimum, the audit system should collect media exportation events for all users and root. Add the following to "/etc/audit/audit.rules: -a always,exit -F arch=b32 -S mount -F auid>=500 -F auid!=4294967295 -k export -a always,exit -F arch=b32 -S mount -F auid=0 -k export If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S mount -F auid>=500 -F auid!=4294967295 -k export -a always,exit -F arch=b64 -S mount -F auid=0 -k export
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208907r603263_rule'
OL6-00-000305: The operating system must provide a near real-time alert when any of the organization defined list of compromise or potential compromise indicators occurs.
To determine that periodic AIDE execution has been scheduled, run the following command: # grep aide /etc/crontab /etc/cron.*/* If there is no output, this is a finding.
Discussion
By default, AIDE does not install itself for periodic execution. Periodically running AIDE may reveal unexpected changes in installed files.
Fix
AIDE should be executed on a periodic basis to check for changes. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check AIDE can be executed periodically through other means; this is merely one example.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219574r603263_rule'
OL6-00-000013: The system package management tool must cryptographically verify the authenticity of system software packages during installation.
To determine whether "yum" is configured to use "gpgcheck", inspect "/etc/yum.conf" and ensure the following appears in the "[main]" section: gpgcheck=1 A value of "1" indicates that "gpgcheck" is enabled. Absence of a "gpgcheck" line or a setting of "0" indicates that it is disabled. If GPG checking is not enabled, this is a finding. If the "yum" system package management tool is not used to update the system, verify with the SA that installed packages are cryptographically signed.
Discussion
Ensuring the validity of packages' cryptographic signatures prior to installation ensures the provenance of the software and protects against malicious tampering.
Fix
The "gpgcheck" option should be used to ensure checking of an RPM package's signature always occurs prior to its installation. To configure yum to check package signatures before installing them, ensure the following line appears in "/etc/yum.conf" in the "[main]" section: gpgcheck=1
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219544r603263_rule'
OL6-00-000274: The system must prohibit the reuse of passwords within five iterations.
To verify the password reuse setting is compliant, run the following command: # grep remember /etc/pam.d/system-auth /etc/pam.d/password-auth The output must be a line beginning with "password required pam_pwhistory.so" and ending with "remember=5". If the line is commented out, the line does not contain the specified elements, or the value for "remember" is less than “5”, this is a finding.
Discussion
Preventing reuse of previous passwords helps ensure that a compromised password is not reused by a user.
Fix
Do not allow users to reuse recent passwords. This can be accomplished by using the "remember" option for the "pam_pwhistory" PAM module. In the file "/etc/pam.d/system-auth", append "remember=5" to the line which refers to the "pam_pwhistory.so" module, as shown: password required pam_pwhistory.so [existing_options] remember=5 The DoD requirement is five passwords.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209012r603263_rule'
OL6-00-000191: The audit system must be configured to audit all discretionary access control permission modifications using fsetxattr.
To determine if the system is configured to audit calls to the "fsetxattr" system call, run the following command: $ sudo grep -w "fsetxattr" /etc/audit/audit.rules -a always,exit -F arch=b32 -S fsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fsetxattr -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S fsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fsetxattr -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "fsetxattr" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S fsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fsetxattr -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S fsetxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fsetxattr -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208900r603263_rule'
OL6-00-000278: The system package management tool must verify permissions on all files and directories associated with the audit package.
The following command will list which audit files on the system have permissions different from what is expected by the RPM database: # rpm -V audit | grep '^.M' If there is any output, for each file or directory found, compare the RPM-expected permissions with the permissions on the file or directory: # rpm -q --queryformat "[%{FILENAMES} %{FILEMODES:perms}\n]" audit | grep [filename] # ls -lL [filename] If the existing permissions are more permissive than those expected by RPM, this is a finding.
Discussion
Permissions on audit binaries and configuration files that are too generous could allow an unauthorized user to gain privileges that they should not have. The permissions set by the vendor should be maintained. Any deviations from this baseline should be investigated.
Fix
The RPM package management system can restore file access permissions of the audit package files and directories. The following command will update audit files with permissions different from what is expected by the RPM database: # rpm --setperms audit
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209014r603263_rule'
OL6-00-000336: The sticky bit must be set on all public directories.
To find world-writable directories that lack the sticky bit, run the following command for each local partition [PART]: # find [PART] -xdev -type d -perm -002 ! -perm -1000 If any world-writable directories are missing the sticky bit, this is a finding.
Discussion
Failing to set the sticky bit on public directories allows unauthorized users to delete files in the directory structure. The only authorized public directories are those temporary directories supplied with the system, or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system, and by users for temporary file storage - such as /tmp - and for directories requiring global read/write access.
Fix
When the so-called 'sticky bit' is set on a directory, only the owner of a given file may remove that file from the directory. Without the sticky bit, any user with write access to a directory may remove any file in the directory. Setting the sticky bit prevents users from removing each other's files. In cases where there is no reason for a directory to be world-writable, a better solution is to remove that permission rather than to set the sticky bit. However, if a directory is used by a particular application, consult that application's documentation instead of blindly changing modes. To set the sticky bit on a world-writable directory [DIR], run the following command: # chmod +t [DIR]
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209038r603263_rule'
OL6-00-000107: The operating system must prevent public IPv6 access into an organizations internal networks, except as appropriately mediated by managed interfaces employing boundary protection devices.
If the system is a cross-domain system, this is not applicable. If IPv6 is disabled, this is not applicable. Run the following command to determine the current status of the "ip6tables" service: # service ip6tables status If the service is not running, it should return the following: ip6tables: Firewall is not running. If the service is not running, this is a finding.
Discussion
The "ip6tables" service provides the system's host-based firewalling capability for IPv6 and ICMPv6.
Fix
The "ip6tables" service can be enabled with the following commands: # chkconfig ip6tables on # service ip6tables start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219550r603263_rule'
OL6-00-000223: The TFTP service must not be running.
To check that the "tftp" service is disabled in system boot configuration, run the following command: # chkconfig "tftp" --list Output should indicate the "tftp" service has either not been installed, or has been disabled, as shown in the example below: # chkconfig "tftp" --list tftp off OR error reading information on service tftp: No such file or directory If the service is running, this is a finding.
Discussion
Disabling the "tftp" service ensures the system is not acting as a tftp server, which does not provide encryption or authentication.
Fix
The "tftp" service should be disabled. The "tftp" service can be disabled with the following command: # chkconfig tftp off
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219559r603263_rule'
OL6-00-000532: The Oracle Linux operating system must mount /dev/shm with the noexec option.
Verify that the "noexec" option is configured for /dev/shm. Check that the operating system is configured to use the "noexec" option for /dev/shm with the following command: # cat /etc/fstab | grep /dev/shm | grep noexec tmpfs /dev/shm tmpfs defaults,nodev,nosuid,noexec 0 0 If the "noexec" option is not present on the line for "/dev/shm", this is a finding. Verify "/dev/shm" is mounted with the "noexec" option: # mount | grep "/dev/shm" | grep noexec If no results are returned, this is a finding.
Discussion
The "noexec" mount option causes the system to not execute binary files. This option must be used for mounting any file system not containing approved binary files as they may be incompatible. Executing files from untrusted file systems increases the opportunity for unprivileged users to attain unauthorized administrative access.
Fix
Configure the "/etc/fstab" to use the "noexec" option for all lines containing "/dev/shm".
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209075r603263_rule'
OL6-00-000216: The rexecd service must not be running.
To check that the "rexec" service is disabled in system boot configuration, run the following command: # chkconfig "rexec" --list Output should indicate the "rexec" service has either not been installed, or has been disabled, as shown in the example below: # chkconfig "rexec" --list rexec off OR error reading information on service rexec: No such file or directory If the service is running, this is a finding.
Discussion
The rexec service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network.
Fix
The "rexec" service, which is available with the "rsh-server" package and runs as a service through xinetd, should be disabled. The "rexec" service can be disabled with the following command: # chkconfig rexec off
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-208916r603263_rule'
OL6-00-000504: The operating system must conduct backups of user-level information contained in the operating system per organization defined frequency to conduct backups consistent with recovery time and recovery point objectives.
Ask an administrator if a process exists to back up user data from the system. If such a process does not exist, this is a finding.
Discussion
Operating system backup is a critical step in maintaining data assurance and availability. User-level information is data generated by information system and/or application users. Backups shall be consistent with organizational recovery time and recovery point objectives.
Fix
Procedures to back up user data from the system must be established and executed. The operating system provides utilities for automating such a process. Commercial and open-source products are also available. Implement a process whereby user data is backed up from the system in accordance with local policies.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219585r603263_rule'
OL6-00-000070: The system must not permit interactive boot.
To check whether interactive boot is disabled, run the following command: $ grep PROMPT /etc/sysconfig/init If interactive boot is disabled, the output will show: PROMPT=no If it does not, this is a finding.
Discussion
Using interactive boot, the console user could disable auditing, firewalls, or other services, weakening system security.
Fix
To disable the ability for users to perform interactive startups, edit the file "/etc/sysconfig/init". Add or correct the line: PROMPT=no The "PROMPT" option allows the console user to perform an interactive system startup, in which it is possible to select the set of services which are started on boot.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208845r603263_rule'
OL6-00-000204: The xinetd service must be uninstalled if no network services utilizing it are enabled.
If network services are using the xinetd service, this is not applicable. Run the following command to determine if the "xinetd" package is installed: # rpm -q xinetd If the package is installed, this is a finding.
Discussion
Removing the "xinetd" package decreases the risk of the xinetd service's accidental (or intentional) activation.
Fix
The "xinetd" package can be uninstalled with the following command: # yum erase xinetd
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208912r603263_rule'
OL6-00-000271: The noexec option must be added to removable media partitions.
Identify any removable media that is configured on the system: # cat /etc/fstab /dev/mapper/vg_rhel6-lv_root / ext4 defaults 1 1 UUID=0be9b205-f8e6-4bf4-b0ba-1f235fc55936 /boot ext4 defaults 1 2 UUID=5D49-30B2 /boot/efi vfat umask=0077,shortname=winnt 0 0 /dev/mapper/vg_rhel6-lv_home /home ext4 defaults 1 2 /dev/mapper/vg_rhel6-lv_tmp /tmp ext4 defaults 1 2 /dev/mapper/vg_rhel6-lv_var /var ext4 defaults 1 2 /dev/mapper/vg_rhel6-lv_swap swap swap defaults 0 0 tmpfs /dev/shm tmpfs defaults 0 0 devpts /dev/pts devpts gid=5,mode=620 0 0 sysfs /sys sysfs defaults 0 0 proc /proc proc defaults 0 0 /dev/sdc1 /media/usb vfat defaults,rw,noexec 0 0 If any of the identified removable media devices do not have "noexec" defined, this is a finding.
Discussion
Allowing users to execute binaries from removable media such as USB keys exposes the system to potential compromise.
Fix
The "noexec" mount option prevents the direct execution of binaries on the mounted filesystem. Users should not be allowed to execute binaries that exist on partitions mounted from removable media (such as a USB key). The "noexec" option prevents code from being executed directly from the media itself, and may therefore provide a line of defense against certain types of worms or malicious code. Add the "noexec" option to the fourth column of "/etc/fstab" for the line which controls mounting of any removable media partitions.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219565r603263_rule'
OL6-00-000315: The Bluetooth kernel module must be disabled.
If the system is configured to prevent the loading of the "bluetooth" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": $ grep -r bluetooth /etc/modprobe.conf /etc/modprobe.d | grep -i “/bin/true” If no line is returned, this is a finding. If the system is configured to prevent the loading of the "net-pf-31" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": $ grep -r net-pf-31 /etc/modprobe.conf /etc/modprobe.d | grep -i “/bin/true” If no line is returned, this is a finding.
Discussion
If Bluetooth functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.
Fix
The kernel's module loading system can be configured to prevent loading of the Bluetooth module. Add the following to the appropriate "/etc/modprobe.d" configuration file to prevent the loading of the Bluetooth module: install net-pf-31 /bin/true install bluetooth /bin/true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219578r603263_rule'
OL6-00-000515: The NFS server must not have the all_squash option enabled.
If the NFS server is read-only, in support of unrestricted access to organizational content, this is not applicable. The related "root_squash" option provides protection against remote administrator-level access to NFS server content. Its use is not a finding. To verify the "all_squash" option has been disabled, run the following command: # grep all_squash /etc/exports If there is output, this is a finding.
Discussion
The "all_squash" option maps all client requests to a single anonymous uid/gid on the NFS server, negating the ability to track file access by user ID.
Fix
Remove any instances of the "all_squash" option from the file "/etc/exports". Restart the NFS daemon for the changes to take effect. # service nfs restart
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209060r603263_rule'
OL6-00-000071: The system must be configured so all network connections associated with a communication session are terminated at the end of the session or after 15 minutes of inactivity from the user at a command prompt, except to fulfill documented and validated mission requirements.
Verify the operating system terminates all network connections associated with a communications session at the end of the session or based on inactivity. Check the value of the system inactivity timeout with the following command: # grep -i tmout /etc/profile.d/* etc/profile.d/tmout.sh:declare -xr TMOUT=900 If "TMOUT" is not set to "900" or less in a script located in the /etc/profile.d/ directory to enforce session termination after inactivity, this is a finding.
Discussion
Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. In addition, quickly terminating an idle session will also free up resources committed by the managed network element. Terminating network connections associated with communications sessions includes, for example, de-allocating associated TCP/IP address/port pairs at the operating system level and de-allocating networking assignments at the application level if multiple application sessions are using a single operating system-level network connection. This does not mean that the operating system terminates all sessions or network access; it only ends the inactive session and releases the resources associated with that session. Satisfies: SRG-OS-000029-GPOS-00010, SRG-OS-000163-GPOS-00072
Fix
Configure the operating system to terminate all network connections associated with a communications session at the end of the session or after a period of inactivity. Create a script to enforce the inactivity timeout (for example /etc/profile.d/tmout.sh) such as: #!/bin/bash declare -xr TMOUT=900
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208846r646940_rule'
OL6-00-000009: The Red Hat Network Service (rhnsd) service must not be running, unless it is being used to query the Oracle Unbreakable Linux Network for updates and information.
If the system needs to automatically communicate with the Oracle Unbreakable Linux Network for updates or information, then this is not applicable. To check that the "rhnsd" service is disabled in system boot configuration, run the following command: # chkconfig "rhnsd" --list Output should indicate the "rhnsd" service has either not been installed or has been disabled at all runlevels, as shown in the example below: # chkconfig "rhnsd" --list "rhnsd" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "rhnsd" is disabled through current runtime configuration: # service rhnsd status If the service is disabled, the command will return the following output: rhnsd is stopped If the service is running, this is a finding.
Discussion
Although systems management and patching is extremely important to system security, management by a system outside the enterprise enclave is not desirable for some environments. However, if the system needs to communicate with the Oracle Unbreakable Linux Network for updates or information, then the "rhnsd" daemon can remain on.
Fix
This service automatically queries the Oracle Unbreakable Linux Network service to determine whether there are any software updates or related information. The "rhnsd" service can be disabled with the following commands: # chkconfig rhnsd off # service rhnsd stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208797r603263_rule'
OL6-00-000160: The system must set a maximum audit log file size.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine how much data the system will retain in each audit log file: "# grep max_log_file /etc/audit/auditd.conf" max_log_file = 6 If the system audit data threshold hasn't been properly set up, this is a finding.
Discussion
The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.
Fix
Determine the amount of audit data (in megabytes) which should be retained in each log file. Edit the file "/etc/audit/auditd.conf". Add or modify the following line, substituting the correct value for [STOREMB]: max_log_file = [STOREMB] Set the value to "6" (MB) or higher for general-purpose systems. Larger values, of course, support retention of even more audit data.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208879r603263_rule'
OL6-00-000227: The SSH daemon must be configured to use only the SSHv2 protocol.
To check which SSH protocol version is allowed, run the following command: # grep Protocol /etc/ssh/sshd_config If configured properly, output should be Protocol 2 If it is not, this is a finding.
Discussion
SSH protocol version 1 suffers from design flaws that result in security vulnerabilities and should not be used.
Fix
Only SSH protocol version 2 connections should be permitted. The default setting in "/etc/ssh/sshd_config" is correct, and can be verified by ensuring that the following line appears: Protocol 2
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-219560r603263_rule'
OL6-00-000030: The system must not allow accounts configured with blank or null passwords.
To verify that null passwords cannot be used, run the following command: # grep nullok /etc/pam.d/system-auth /etc/pam.d/password-auth If this produces any output, it may be possible to log on to accounts with empty passwords. If null passwords can be used, this is a finding.
Discussion
If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.
Fix
If an account is configured for password authentication but does not have an assigned password, it may be possible to log on to the account without authentication. Remove any instances of the "nullok" option in "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" to prevent logons with empty passwords.
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-208807r603263_rule'
OL6-00-000372: The operating system, upon successful logon/access, must display to the user the number of unsuccessful logon/access attempts since the last successful logon/access.
To ensure that last logon/access notification is configured correctly, run the following command: # grep pam_lastlog.so /etc/pam.d/system-auth The output should show output "showfailed". If that is not the case, this is a finding.
Discussion
Users need to be aware of activity that occurs regarding their account. Providing users with information regarding the number of unsuccessful attempts that were made to login to their account allows the user to determine if any unauthorized activity has occurred and gives them an opportunity to notify administrators.
Fix
To configure the system to notify users of last logon/access using "pam_lastlog", add the following line immediately after "session required pam_limits.so": session required pam_lastlog.so showfailed
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209052r603263_rule'
OL6-00-000270: Remote file systems must be mounted with the nosuid option.
To verify the "nosuid" option is configured for all NFS mounts, run the following command: $ mount | grep nfs All NFS mounts should show the "nosuid" setting in parentheses, along with other mount options. If the setting does not show, this is a finding.
Discussion
NFS mounts should not present suid binaries to users. Only vendor-supplied suid executables should be installed to their default location on the local filesystem.
Fix
Add the "nosuid" option to the fourth column of "/etc/fstab" for the line which controls mounting of any NFS mounts.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209009r603263_rule'
OL6-00-000282: There must be no world-writable files on the system.
To find world-writable files, run the following command for each local partition [PART], excluding special filesystems such as /selinux, /proc, or /sys: # find [PART] -xdev -type f -perm -002 If there is output, this is a finding.
Discussion
Data in world-writable files can be modified by any user on the system. In almost all circumstances, files can be configured using a combination of user and group permissions to support whatever legitimate access is needed without the risk caused by world-writable files.
Fix
It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor for recurring world-writable files, as these may be symptoms of a misconfigured application or user account.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209018r603263_rule'
OL6-00-000046: Library files must be owned by a system account.
System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: /lib /lib64 /usr/lib /usr/lib64 /usr/local/lib /usr/local/lib64 Kernel modules, which can be added to the kernel during runtime, are stored in "/lib/modules". All files in these directories should not be group-writable or world-writable. To find shared libraries that are not owned by "root" and do not match what is expected by the RPM, run the following command: for i in /lib /lib64 /usr/lib /usr/lib64 /usr/local/lib /usr/local/lib64 do for j in `find -L $i \! -user root` do rpm -V -f $j | grep '^.....U' done done If the command returns any results, this is a finding.
Discussion
Files from shared library directories are loaded into the address space of processes (including privileged ones) or of the kernel itself at runtime. Proper ownership is necessary to protect the integrity of the system.
Fix
System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: /lib /lib64 /usr/lib /usr/lib64 /usr/local/lib /usr/local/lib64 If any file in these directories is found to be owned by a user other than “root” and does not match what is expected by the RPM, correct its ownership by running one of the following commands: # rpm --setugids [PACKAGE_NAME] Or # chown root [FILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208823r603263_rule'
OL6-00-000280: The system package management tool must verify group-ownership on all files and directories associated with the audit package.
The following command will list which audit files on the system have group-ownership different from what is expected by the RPM database: # rpm -V audit | grep '^......G' If there is output, this is a finding.
Discussion
Group-ownership of audit binaries and configuration files that is incorrect could allow an unauthorized user to gain privileges that they should not have. The group-ownership set by the vendor should be maintained. Any deviations from this baseline should be investigated.
Fix
The RPM package management system can restore file group-ownership of the audit package files and directories. The following command will update audit files with group-ownership different from what is expected by the RPM database: # rpm --setugids audit
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209016r603263_rule'
OL6-00-000003: The system must use a separate file system for /var/log.
Run the following command to determine if "/var/log" is on its own partition or logical volume: $ mount | grep "on /var/log " If "/var/log" has its own partition or volume group, a line will be returned. If no line is returned, this is a finding.
Discussion
Placing "/var/log" in its own partition enables better separation between log files and other files in "/var/".
Fix
System logs are stored in the "/var/log" directory. Ensure that it has its own partition or logical volume at installation time, or migrate it using LVM.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208795r603263_rule'
OL6-00-000385: Audit log directories must have mode 0755 or less permissive.
Run the following command to check the mode of the system audit directories: grep "^log_file" /etc/audit/auditd.conf|sed 's/^[^/]*//; s/[^/]*$//'|xargs stat -c %a:%n Audit directories must be mode 0755 or less permissive. If any are more permissive, this is a finding.
Discussion
If users can delete audit logs, audit trails can be modified or destroyed.
Fix
Change the mode of the audit log directories with the following command: # chmod go-w [audit_directory]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209055r603263_rule'
OL6-00-000321: The system must provide VPN connectivity for communications over untrusted networks.
If the system does not communicate over untrusted networks, this is not applicable. Run the following command to determine if the "libreswan" package is installed: # rpm -q libreswan If the package is not installed, this is a finding.
Discussion
Providing the ability for remote users or systems to initiate a secure VPN connection protects information when it is transmitted over a wide area network.
Fix
The Libreswan package provides an implementation of IPsec and IKE, which permits the creation of secure tunnels over untrusted networks. The "libreswan" package can be installed with the following command: # yum install libreswan
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219580r603263_rule'
OL6-00-000048: All system command files must be owned by root.
System executables are stored in the following directories by default: /bin /usr/bin /usr/local/bin /sbin /usr/sbin /usr/local/sbin To find system executables that are not owned by "root", run the following command for each directory [DIR] which contains system executables: $ find -L [DIR] \! -user root If any system executables are found to not be owned by root, this is a finding.
Discussion
System binaries are executed by privileged users as well as system services, and restrictive permissions are necessary to ensure that their execution of these programs cannot be co-opted.
Fix
System executables are stored in the following directories by default: /bin /usr/bin /usr/local/bin /sbin /usr/sbin /usr/local/sbin If any file [FILE] in these directories is found to be owned by a user other than root, correct its ownership with the following command: # chown root [FILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208825r603263_rule'
OL6-00-000331: The Bluetooth service must be disabled.
To check that the "bluetooth" service is disabled in system boot configuration, run the following command: # chkconfig "bluetooth" --list Output should indicate the "bluetooth" service has either not been installed or has been disabled at all runlevels, as shown in the example below: # chkconfig "bluetooth" --list "bluetooth" 0:off 1:off 2:off 3:off 4:off 5:off 6:off If the service is configured to run, this is a finding.
Discussion
Disabling the "bluetooth" service prevents the system from attempting connections to Bluetooth devices, which entails some security risk. Nevertheless, variation in this risk decision may be expected due to the utility of Bluetooth connectivity and its limited range.
Fix
The "bluetooth" service can be disabled with the following command: # chkconfig bluetooth off # service bluetooth stop
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219581r603263_rule'
OL6-00-000228: The Oracle Linux operating system must be configured so that the SSH daemon is configured to only use Message Authentication Codes (MACs) employing FIPS 140-2 approved cryptographic hash algorithms.
Verify the SSH daemon is configured to only use MACs employing FIPS 140-2-approved hashes. Note: If OL6-00-000534 is a finding, this is automatically a finding as the system cannot implement FIPS 140-2-approved cryptographic algorithms and hashes. Check that the SSH daemon is configured to only use MACs employing FIPS 140-2-approved hashes with the following command: # grep -i macs /etc/ssh/sshd_config MACs hmac-sha2-512,hmac-sha2-256 If any hashes other than "hmac-sha2-512" or "hmac-sha2-256" are listed, the order differs from the example above, they are missing, or the returned line is commented out, this is a finding.
Discussion
DoD information systems are required to use FIPS 140-2 approved cryptographic hash functions. The only SSHv2 hash algorithm meeting this requirement is SHA. The system will attempt to use the first hash presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest hash available to secure the SSH connection.
Fix
Edit the "/etc/ssh/sshd_config" file to uncomment or add the line for the "MACs" keyword and set its value to "hmac-sha2-512, hmac-sha2-256" (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor): MACs hmac-sha2-512,hmac-sha2-256 The SSH service must be restarted for changes to take effect. # sudo service sshd restart
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219958r744068_rule'
OL6-00-000218: The rlogind service must not be running.
To check that the "rlogin" service is disabled in system boot configuration, run the following command: # chkconfig "rlogin" --list Output should indicate the "rlogin" service has either not been installed, or has been disabled, as shown in the example below: # chkconfig "rlogin" --list rlogin off OR error reading information on service rlogin: No such file or directory If the service is running, this is a finding.
Discussion
The rlogin service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network.
Fix
The "rlogin" service, which is available with the "rsh-server" package and runs as a service through xinetd, should be disabled. The "rlogin" service can be disabled with the following command: # chkconfig rlogin off
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-219558r603263_rule'
OL6-00-000357: The system must disable accounts after excessive login failures within a 15-minute interval.
To ensure the failed password attempt policy is configured correctly, run the following command: $ grep pam_faillock /etc/pam.d/system-auth /etc/pam.d/password-auth For each file, the output should show "fail_interval=<interval-in-seconds>" where "interval-in-seconds" is 900 (15 minutes) or greater. If the "fail_interval" parameter is not set, the default setting of 900 seconds is acceptable. If that is not the case, this is a finding.
Discussion
Locking out user accounts after a number of incorrect attempts within a specific period of time prevents direct password guessing attacks.
Fix
Utilizing "pam_faillock.so", the "fail_interval" directive configures the system to lock out accounts after a number of incorrect logon attempts. Modify the content of both "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" as follows: Add the following line immediately before the "pam_unix.so" statement in the "AUTH" section: auth required pam_faillock.so preauth silent deny=3 unlock_time=900 fail_interval=900 Add the following line immediately after the "pam_unix.so" statement in the "AUTH" section: auth [default=die] pam_faillock.so authfail deny=3 unlock_time=900 fail_interval=900 Add the following line immediately before the "pam_unix.so" statement in the "ACCOUNT" section: account required pam_faillock.so Note that any updates made to "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" may be overwritten by the "authconfig" program. The "authconfig" program should not be used.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219583r603263_rule'
OL6-00-000134: All rsyslog-generated log files must be group-owned by root.
The group-owner of all log files written by "rsyslog" should be root. These log files are determined by the second part of each Rule line in "/etc/rsyslog.conf" and typically all appear in "/var/log". To see the group-owner of a given log file, run the following command: $ ls -l [LOGFILE] Some log files referenced in /etc/rsyslog.conf may be created by other programs and may require exclusion from consideration. If the group-owner is not root, this is a finding.
Discussion
The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
Fix
The group-owner of all log files written by "rsyslog" should be root. These log files are determined by the second part of each Rule line in "/etc/rsyslog.conf" and typically all appear in "/var/log". For each log file [LOGFILE] referenced in "/etc/rsyslog.conf", run the following command to inspect the file's group owner: $ ls -l [LOGFILE] If the owner is not "root", run the following command to correct this: # chgrp root [LOGFILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208871r603263_rule'
OL6-00-000256: The openldap-servers package must not be installed unless required.
To verify the "openldap-servers" package is not installed, run the following command: $ rpm -q openldap-servers The output should show the following. package openldap-servers is not installed If it does not, this is a finding.
Discussion
Unnecessary packages should not be installed to decrease the attack surface of the system.
Fix
The "openldap-servers" package should be removed if not in use. Is this machine the OpenLDAP server? If not, remove the package. # yum erase openldap-servers The openldap-servers RPM may be installed. It is needed only by the OpenLDAP server, not by clients which use LDAP for authentication. If the system is not intended for use as an LDAP server, it should be removed.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208932r603263_rule'
OL6-00-000516: The system package management tool must verify ownership on all files and directories associated with packages.
The following command will list which files on the system have ownership different from what is expected by the RPM database: # rpm -Va | grep '^.....U' If any output is produced, verify that the changes were due to STIG application and have been documented with the ISSO. If any output has not been documented with the ISSO, this is a finding.
Discussion
Ownership of system binaries and configuration files that is incorrect could allow an unauthorized user to gain privileges that they should not have. The ownership set by the vendor should be maintained. Any deviations from this baseline should be investigated.
Fix
The RPM package management system can restore ownership of package files and directories. The following command will update files and directories with ownership different from what is expected by the RPM database: # rpm -qf [file or directory name] # rpm --setugids [package]
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209061r603263_rule'
OL6-00-000334: Accounts must be locked upon 35 days of inactivity.
To verify the "INACTIVE" setting, run the following command: grep "INACTIVE" /etc/default/useradd The output should indicate the "INACTIVE" configuration option is set to an appropriate integer as shown in the example below: # grep "INACTIVE" /etc/default/useradd INACTIVE=35 If it does not, this is a finding.
Discussion
Disabling inactive accounts ensures that accounts which may not have been responsibly removed are not available to attackers who may have compromised their credentials.
Fix
To specify the number of days after a password expires (which signifies inactivity) until an account is permanently disabled, add or correct the following lines in "/etc/default/useradd", substituting "[NUM_DAYS]" appropriately: INACTIVE=[NUM_DAYS] A value of 35 is recommended. If a password is currently on the verge of expiration, then 35 days remain until the account is automatically disabled. However, if the password will not expire for another 60 days, then 95 days could elapse until the account would be automatically disabled. See the "useradd" man page for more information. Determining the inactivity timeout must be done with careful consideration of the length of a "normal" period of inactivity for users in the particular environment. Setting the timeout too low incurs support costs and also has the potential to impact availability of the system to legitimate users.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209036r603263_rule'
OL6-00-000534: The Oracle Linux 6 operating system must implement NIST FIPS-validated cryptography for the following: to provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards.
Verify the operating system implements DoD-approved encryption to protect the confidentiality of remote access sessions. Check to see if the "dracut-fips" package is installed with the following command: # yum list installed dracut-fips dracut-fips-004-411.el6.noarch.rpm If a "dracut-fips" package is installed, check to see if the kernel command line is configured to use FIPS mode with the following command: # grep fips /boot/grub/grub.conf kernel /boot/vmlinuz-4.1.12-124.18.5.el6uek.x86_64 ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=uk LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16 rd_LVM_LV=VolGroup/lv_root rd_NO_DM rhgb quiet fips=1 boot=/dev/sda1 If the kernel command line is configured to use FIPS mode, check to see if the system is in FIPS mode with the following command: # cat /proc/sys/crypto/fips_enabled 1 If a "dracut-fips" package is not installed, the kernel command line does not have a fips entry, or the system has a value of "0" for "fips_enabled" in "/proc/sys/crypto", this is a finding.
Discussion
Use of weak or untested encryption algorithms undermines the purposes of using encryption to protect data. The operating system must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated. Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000185-GPOS-00079, SRG-OS-000396-GPOS-00176, SRG-OS-000405-GPOS-00184, SRG-OS-000478-GPOS-00223
Fix
Configure the operating system to implement DoD-approved encryption by installing the dracut-fips package. To enable strict FIPS compliance, the fips=1 kernel option needs to be added to the kernel command line during system installation so key generation is done with FIPS-approved algorithms and continuous monitoring tests in place. Configure the operating system to implement DoD-approved encryption by following the steps below: The fips=1 kernel option needs to be added to the kernel command line during system installation so that key generation is done with FIPS-approved algorithms and continuous monitoring tests in place. Users should also ensure that the system has plenty of entropy during the installation process by moving the mouse around, or if no mouse is available, ensuring that many keystrokes are typed. The recommended amount of keystrokes is 256 and more. Less than 256 keystrokes may generate a non-unique key. Install the dracut-fips package with the following command: # yum install dracut-fips Existing prelinking, if any, should be undone on all system files using the following command: # prelink -u -a Recreate the "initramfs" file with the following command: Note: This command will overwrite the existing "initramfs" file. # dracut -f Modify the kernel command line of the current kernel in the "grub.conf" file by adding the following option to the "grub.conf" file: fips=1 If /boot or /boot/efi reside on separate partitions, the kernel parameter boot=<partition of /boot or /boot/efi> must be added to the kernel command line. You can identify a partition by running the df /boot or df /boot/efi command: # df /boot Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda1 495844 53780 416464 12% /boot To ensure the "boot=" configuration option will work even if device naming changes occur between boots, identify the universally unique identifier (UUID) of the partition with the following command: # blkid /dev/sda1 /dev/sda1: UUID="05c000f1-a213-759e-c7a2-f11b7424c797" TYPE="ext4" For the example above, append the following string to the kernel command line: boot=UUID=05c000f1-a213-759e-c7a2-f11b7424c797 Reboot the system for the changes to take effect.
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-209076r603263_rule'
OL6-00-000059: The system must require passwords to contain at least one lower-case alphabetic character.
To check how many lower-case characters are required in a password, run the following command: $ grep pam_cracklib /etc/pam.d/system-auth /etc/pam.d/password-auth The "lcredit" parameter (as a negative number) will indicate how many lower-case characters are required. The DoD requires at least one lower-case character in a password. This would appear as "lcredit=-1". If the “lcredit” parameter is not found or not set to the required value, this is a finding.
Discussion
Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.
Fix
The pam_cracklib module's "lcredit=" parameter controls requirements for usage of lower-case letters in a password. When set to a negative number, any password will be required to contain that many lower-case characters. Edit /etc/pam.d/system-auth and /etc/pam.d/password-auth adding "lcredit=-1" after pam_cracklib.so to require use of a lower-case character in passwords.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208834r603263_rule'
OL6-00-000526: Automated file system mounting tools must not be enabled unless needed.
To verify the "autofs" service is disabled, run the following command: chkconfig --list autofs If properly configured, the output should be the following: autofs 0:off 1:off 2:off 3:off 4:off 5:off 6:off Verify the "autofs" service is not running: # service autofs status If the autofs service is enabled or running, this is a finding.
Discussion
All filesystems that are required for the successful operation of the system should be explicitly listed in "/etc/fstab" by an administrator. New filesystems should not be arbitrarily introduced via the automounter. The "autofs" daemon mounts and unmounts filesystems, such as user home directories shared via NFS, on demand. In addition, autofs can be used to handle removable media, and the default configuration provides the cdrom device as "/misc/cd". However, this method of providing access to removable media is not common, so autofs can almost always be disabled if NFS is not in use. Even if NFS is required, it is almost always possible to configure filesystem mounts statically by editing "/etc/fstab" rather than relying on the automounter.
Fix
If the "autofs" service is not needed to dynamically mount NFS filesystems or removable media, disable the service for all runlevels: # chkconfig --level 0123456 autofs off Stop the service if it is already running: # service autofs stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209069r603263_rule'
OL6-00-000034: The /etc/shadow file must be group-owned by root.
To check the group ownership of "/etc/shadow", run the command: $ ls -l /etc/shadow If properly configured, the output should indicate the following group-owner. "root" If it does not, this is a finding.
Discussion
The "/etc/shadow" file stores password hashes. Protection of this file is critical for system security.
Fix
To properly set the group owner of "/etc/shadow", run the command: # chgrp root /etc/shadow
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208811r603263_rule'
OL6-00-000384: Audit log files must be owned by root.
Run the following command to check the owner of the system audit logs: grep "^log_file" /etc/audit/auditd.conf|sed s/^[^\/]*//|xargs stat -c %U:%n Audit logs must be owned by root. If they are not, this is a finding.
Discussion
If non-privileged users can write to audit logs, audit trails can be modified or destroyed.
Fix
Change the owner of the audit log files with the following command: # chown root [audit_file]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209054r603263_rule'
OL6-00-000035: The /etc/shadow file must have mode 0000.
To check the permissions of "/etc/shadow", run the command: $ ls -l /etc/shadow If properly configured, the output should indicate the following permissions: "----------" If it does not, this is a finding.
Discussion
The "/etc/shadow" file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.
Fix
To properly set the permissions of "/etc/shadow", run the command: # chmod 0000 /etc/shadow
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208812r603263_rule'
OL6-00-000165: The audit system must be configured to audit all attempts to alter system time through adjtimex.
To determine if the system is configured to audit calls to the "adjtimex" system call, run the following command: $ sudo grep -w "adjtimex" /etc/audit/audit.rules -a always,exit -F arch=b32 -S adjtimex -k audit_time_rules -a always,exit -F arch=b64 -S adjtimex -k audit_time_rules If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "adjtimex" system call, this is a finding.
Discussion
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
Fix
On a 32-bit system, add the following to "/etc/audit/audit.rules": # audit_time_rules -a always,exit -F arch=b32 -S adjtimex -k audit_time_rules If the system is 64-bit, then also add the following: # audit_time_rules -a always,exit -F arch=b64 -S adjtimex -k audit_time_rules
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208882r603263_rule'
OL6-00-000023: The system must use a Linux Security Module configured to limit the privileges of system services.
Check the file "/etc/selinux/config" and ensure the following line appears: SELINUXTYPE=targeted If it does not, this is a finding.
Discussion
Setting the SELinux policy to "targeted" or a more specialized policy ensures the system will confine processes that are likely to be targeted for exploitation, such as network or system services.
Fix
The SELinux "targeted" policy is appropriate for general-purpose desktops and servers, as well as systems in many other roles. To configure the system to use this policy, add or correct the following line in "/etc/selinux/config": SELINUXTYPE=targeted Other policies, such as "mls", provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208802r603263_rule'
OL6-00-000294: All GIDs referenced in /etc/passwd must be defined in /etc/group.
To ensure all GIDs referenced in /etc/passwd are defined in /etc/group, run the following command: # pwck -r | grep 'no group' There should be no output. If there is output, this is a finding.
Discussion
Inconsistency in GIDs between /etc/passwd and /etc/group could lead to a user having unintended rights.
Fix
Add a group to the system for each GID referenced without a corresponding group.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209025r603263_rule'
OL6-00-000304: The operating system must employ automated mechanisms to detect the presence of unauthorized software on organizational information systems and notify designated organizational officials in accordance with the organization defined frequency.
To determine that periodic AIDE execution has been scheduled, run the following command: # grep aide /etc/crontab /etc/cron.*/* If there is no output, this is a finding.
Discussion
By default, AIDE does not install itself for periodic execution. Periodically running AIDE may reveal unexpected changes in installed files.
Fix
AIDE should be executed on a periodic basis to check for changes. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check AIDE can be executed periodically through other means; this is merely one example.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219573r603263_rule'
OL6-00-000082: IP forwarding for IPv4 must not be enabled, unless the system is a router.
The status of the "net.ipv4.ip_forward" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.ip_forward The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.ip_forward /etc/sysctl.conf The ability to forward packets is only appropriate for routers. If the correct value is not returned, this is a finding.
Discussion
IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for systems acting as routers.
Fix
To set the runtime status of the "net.ipv4.ip_forward" kernel parameter, run the following command: # sysctl -w net.ipv4.ip_forward=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.ip_forward = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208852r603263_rule'
OL6-00-000126: The Reliable Datagram Sockets (RDS) protocol must be disabled unless required.
If the system is configured to prevent the loading of the "rds" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module-loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": $ grep -r rds /etc/modprobe.conf /etc/modprobe.d If no line is returned, this is a finding. This is not a finding if the RDS service is required for proper system or application operation. Oracle Engineered Systems such as Exadata use the RDS service for InfiniBand-based communication with storage services.
Discussion
Disabling RDS protects the system against exploitation of any flaws in its implementation.
Fix
The Reliable Datagram Sockets (RDS) protocol is a transport layer protocol designed to provide reliable high- bandwidth, low-latency communications between nodes in a cluster. To configure the system to prevent the "rds" kernel module from being loaded, add the following line to a file in the directory "/etc/modprobe.d": install rds /bin/true
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208868r603263_rule'
OL6-00-000018: A file integrity baseline must be created.
To find the location of the AIDE database file, run the following command: # grep DBDIR /etc/aide.conf Using the defined values of the [DBDIR] and [database] variables, verify the existence of the AIDE database file: # ls -l [DBDIR]/[database_file_name] If there is no database file, this is a finding.
Discussion
For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files.
Fix
Run the following command to generate a new database: # /usr/sbin/aide --init By default, the database will be written to the file "/var/lib/aide/aide.db.new.gz". Storing the database, the configuration file "/etc/aide.conf", and the binary "/usr/sbin/aide" (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows: # cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz To initiate a manual check, run the following command: # /usr/sbin/aide --check If this check produces any unexpected output, investigate.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208800r603263_rule'
OL6-00-000054: Users must be warned 7 days in advance of password expiration.
To check the password warning age, run the command: $ grep PASS_WARN_AGE /etc/login.defs The DoD requirement is 7. If it is not set to the required value, this is a finding.
Discussion
Setting the password warning age enables users to make the change at a practical time.
Fix
To specify how many days prior to password expiration that a warning will be issued to users, edit the file "/etc/login.defs" and add or correct the following line, replacing [DAYS] appropriately: PASS_WARN_AGE [DAYS] The DoD requirement is 7.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208829r603263_rule'
OL6-00-000335: The operating system must manage information system identifiers for users and devices by disabling the user identifier after an organization defined time period of inactivity.
To verify the "INACTIVE" setting, run the following command: grep "INACTIVE" /etc/default/useradd The output should indicate the "INACTIVE" configuration option is set to an appropriate integer as shown in the example below: # grep "INACTIVE" /etc/default/useradd INACTIVE=35 If it does not, this is a finding.
Discussion
Disabling inactive accounts ensures that accounts which may not have been responsibly removed are not available to attackers who may have compromised their credentials.
Fix
To specify the number of days after a password expires (which signifies inactivity) until an account is permanently disabled, add or correct the following lines in "/etc/default/useradd", substituting "[NUM_DAYS]" appropriately: INACTIVE=[NUM_DAYS] A value of 35 is recommended. If a password is currently on the verge of expiration, then 35 days remain until the account is automatically disabled. However, if the password will not expire for another 60 days, then 95 days could elapse until the account would be automatically disabled. See the "useradd" man page for more information. Determining the inactivity timeout must be done with careful consideration of the length of a "normal" period of inactivity for users in the particular environment. Setting the timeout too low incurs support costs and also has the potential to impact availability of the system to legitimate users.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209037r603263_rule'
OL6-00-000326: The Department of Defense (DoD) login banner must be displayed immediately prior to, or as part of, graphical desktop environment login prompts.
If the GConf2 package is not installed, this is not applicable. To ensure login warning banner text is properly set, run the following: $ gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gdm/simple-greeter/banner_message_text If properly configured, the proper banner text will appear within this schema. The DoD required text is either: "You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details." OR: "I've read & consent to terms in IS user agreem't." If the DoD required banner text does not appear in the schema, this is a finding.
Discussion
An appropriate warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers.
Fix
To set the text shown by the GNOME Display Manager in the login screen, run the following command: # gconftool-2 --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type string \ --set /apps/gdm/simple-greeter/banner_message_text \ "[DoD required text]" Where the DoD required text is either: "You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details." OR: "I've read & consent to terms in IS user agreem't." When entering a warning banner that spans several lines, remember to begin and end the string with """. This command writes directly to the file "/etc/gconf/gconf.xml.mandatory/apps/gdm/simple-greeter/%gconf.xml", and this file can later be edited directly if necessary.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209035r603263_rule'
OL6-00-000169: The audit system must be configured to audit all attempts to alter system time through stime.
If the system is 64-bit only, this is not applicable. To determine if the system is configured to audit calls to the "stime" system call, run the following command: $ sudo grep -w "stime" /etc/audit/audit.rules -a always,exit -F arch=b32 -S stime -k audit_time_rules If the system is not configured to audit the "stime" system call, this is a finding.
Discussion
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
Fix
On a 32-bit system, add the following to "/etc/audit/audit.rules": # audit_time_rules -a always,exit -F arch=b32 -S stime -k audit_time_rules Note: On a 64-bit system, it is not necessary to define a rule for "stime".
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208884r603263_rule'
OL6-00-000058: The system must require passwords to contain at least one special character.
To check how many special characters are required in a password, run the following command: $ grep pam_cracklib /etc/pam.d/system-auth /etc/pam.d/password-auth The "ocredit" parameter (as a negative number) will indicate how many special characters are required. The DoD requires at least one special character in a password. This would appear as "ocredit=-1". If the “ocredit” parameter is not found or not set to the required value, this is a finding.
Discussion
Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space.
Fix
The pam_cracklib module's "ocredit=" parameter controls requirements for usage of special (or ``other'') characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_cracklib will grant +1 additional length credit for each special character. Edit /etc/pam.d/system-auth and /etc/pam.d/password-auth adding "ocredit=-1" after pam_cracklib.so to require use of a special character in passwords.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208833r603263_rule'
OL6-00-000249: Mail relaying must be restricted.
If the system is an authorized mail relay host, this is not applicable. Run the following command to ensure postfix accepts mail messages from only the local system: $ grep inet_interfaces /etc/postfix/main.cf If properly configured, the output should show only "localhost". If it does not, this is a finding.
Discussion
This ensures "postfix" accepts mail messages (such as cron job reports) from the local system only, and not from the network, which protects it from network attack.
Fix
Edit the file "/etc/postfix/main.cf" to ensure that only the following "inet_interfaces" line appears: inet_interfaces = localhost
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208930r603263_rule'
OL6-00-000337: All public directories must be owned by a system account.
The following command will discover and print world-writable directories that are not owned by a system account, given the assumption that only system accounts have a uid lower than 500. Run it once for each local partition [PART]: # find [PART] -xdev -type d -perm -0002 -uid +500 -print If there is output, this is a finding.
Discussion
Allowing a user account to own a world-writable directory is undesirable because it allows the owner of that directory to remove or replace any files that may be placed in the directory by other users.
Fix
All directories in local partitions which are world-writable should be owned by root or another system account. If any world-writable directories are not owned by a system account, this should be investigated. Following this, the files should be deleted or assigned to an appropriate group.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209039r603263_rule'
OL6-00-000073: The Department of Defense (DoD) login banner must be displayed immediately prior to, or as part of, console login prompts.
To check if the system login banner is compliant, run the following command: $ cat /etc/issue Note: The full text banner must be implemented unless there are character limitations that prevent the display of the full DoD logon banner. If the required DoD logon banner is not displayed, this is a finding.
Discussion
An appropriate warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers.
Fix
To configure the system login banner: Edit "/etc/issue". Replace the default text with a message compliant with the local site policy or a legal disclaimer. The DoD required text is either: "You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details." If the device cannot support the full DoD logon banner due to character limitations, the following text can be used: "I've read & consent to terms in IS user agreem't."
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208847r603263_rule'
OL6-00-000096: The system must use a reverse-path filter for IPv4 network traffic when possible on all interfaces.
The status of the "net.ipv4.conf.all.rp_filter" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.rp_filter The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.all.rp_filter /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.
Fix
To set the runtime status of the "net.ipv4.conf.all.rp_filter" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.rp_filter=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.rp_filter = 1
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208863r603263_rule'
OL6-00-000176: The operating system must automatically audit account disabling actions.
To determine if the system is configured to audit account changes, run the following command: $sudo egrep -w '(/etc/passwd|/etc/shadow|/etc/group|/etc/gshadow|/etc/security/opasswd)' /etc/audit/audit.rules If the system is configured to watch for account changes, lines should be returned for each file specified (and with "-p wa" for each). If the system is not configured to audit account changes, this is a finding.
Discussion
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
Fix
Add the following to "/etc/audit/audit.rules", in order to capture events that modify account changes: # audit_account_changes -w /etc/group -p wa -k audit_account_changes -w /etc/passwd -p wa -k audit_account_changes -w /etc/gshadow -p wa -k audit_account_changes -w /etc/shadow -p wa -k audit_account_changes -w /etc/security/opasswd -p wa -k audit_account_changes
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208889r603263_rule'
OL6-00-000302: A file integrity tool must be used at least weekly to check for unauthorized file changes, particularly the addition of unauthorized system libraries or binaries, or for unauthorized modification to authorized system libraries or binaries.
To determine that periodic AIDE execution has been scheduled, run the following command: # grep aide /etc/crontab /etc/cron.*/* If there is no output, or if aide is not run at least weekly, this is a finding.
Discussion
By default, AIDE does not install itself for periodic execution. Periodically running AIDE may reveal unexpected changes in installed files.
Fix
AIDE should be executed on a periodic basis to check for changes. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check AIDE can be executed periodically through other means; this is merely one example.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219571r603263_rule'
OL6-00-000234: The SSH daemon must ignore .rhosts files.
To determine how the SSH daemon's "IgnoreRhosts" option is set, run the following command: # grep -i IgnoreRhosts /etc/ssh/sshd_config If no line, a commented line, or a line indicating the value "yes" is returned, then the required value is set. If the required value is not set, this is a finding.
Discussion
SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.
Fix
SSH can emulate the behavior of the obsolete rsh command in allowing users to enable insecure access to their accounts via ".rhosts" files. To ensure this behavior is disabled, add or correct the following line in "/etc/ssh/sshd_config": IgnoreRhosts yes
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208923r603263_rule'
OL6-00-000192: The audit system must be configured to audit all discretionary access control permission modifications using lchown.
To determine if the system is configured to audit calls to the "lchown" system call, run the following command: $ sudo grep -w "lchown" /etc/audit/audit.rules -a always,exit -F arch=b32 -S lchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S lchown -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S lchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S lchown -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "lchown" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S lchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S lchown -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S lchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S lchown -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208901r603263_rule'
OL6-00-000290: X Windows must not be enabled unless required.
To verify the default runlevel is 3, run the following command: # grep initdefault /etc/inittab The output should show the following: id:3:initdefault: If it does not, this is a finding.
Discussion
Unnecessary services should be disabled to decrease the attack surface of the system.
Fix
Setting the system's runlevel to 3 will prevent automatic startup of the X server. To do so, ensure the following line in "/etc/inittab" features a "3" as shown: id:3:initdefault:
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219569r603263_rule'
OL6-00-000248: The system clock must be synchronized to an authoritative DoD time source.
A remote NTP server should be configured for time synchronization. To verify one is configured, open the following file. /etc/ntp.conf In the file, there should be a section similar to the following: # --- OUR TIMESERVERS ----- server [ntpserver] If this is not the case, this is a finding.
Discussion
Synchronizing with an NTP server makes it possible to collate system logs from multiple sources or correlate computer events with real time events. Using a trusted NTP server provided by your organization is recommended.
Fix
To specify a remote NTP server for time synchronization, edit the file "/etc/ntp.conf". Add or correct the following lines, substituting the IP or hostname of a remote NTP server for ntpserver. server [ntpserver] This instructs the NTP software to contact that remote server to obtain time data.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219563r603263_rule'
OL6-00-000213: The rsh-server package must not be installed.
Run the following command to determine if the "rsh-server" package is installed: # rpm -q rsh-server If the package is installed, this is a finding.
Discussion
The "rsh-server" package provides several obsolete and insecure network services. Removing it decreases the risk of those services' accidental (or intentional) activation.
Fix
The "rsh-server" package can be uninstalled with the following command: # yum erase rsh-server
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-208914r603263_rule'
OL6-00-000068: The system boot loader must require authentication.
To verify the boot loader password has been set and encrypted, run the following command: # grep password /boot/grub/grub.conf The output should show the following: password --encrypted $6$[rest-of-the-password-hash] If it does not, this is a finding.
Discussion
Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode.
Fix
The grub boot loader should have password protection enabled to protect boot-time settings. To do so, select a password and then generate a hash from it by running the following command: # grub-crypt --sha-512 When prompted to enter a password, insert the following line into "/boot/grub/grub.conf" immediately after the header comments. (Use the output from "grub-crypt" as the value of [password-hash]): password --encrypted [password-hash]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208843r603263_rule'
OL6-00-000299: The system must require passwords to contain no more than three consecutive repeating characters.
To check the maximum value for consecutive repeating characters, run the following command: $ grep pam_cracklib /etc/pam.d/system-auth /etc/pam.d/password-auth Look for the value of the "maxrepeat" parameter. The DoD requirement is “3”. If "maxrepeat" is not found, is set to zero, or is set to a value greater than “3”, this is a finding.
Discussion
Passwords with excessive repeating characters may be more vulnerable to password-guessing attacks.
Fix
The pam_cracklib module's ”maxrepeat” parameter controls requirements for consecutive repeating characters. When set to a positive number, it will reject passwords that contain more than the number of consecutive characters. Edit /etc/pam.d/system-auth and /etc/pam.d/password-auth adding "maxrepeat=3" after pam_cracklib.so to prevent a run of (3 + 1) or more identical characters. password required pam_cracklib.so maxrepeat=3
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209029r603263_rule'
OL6-00-000197: The audit system must be configured to audit failed attempts to access files and programs.
To verify that the audit system collects unauthorized file accesses, run the following commands: # grep EACCES /etc/audit/audit.rules -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid=0 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid=0 -k access # grep EPERM /etc/audit/audit.rules -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid=0 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid=0 -k access If the system is 64-bit and does not return rules for both "b32" and "b64" architectures, this is a finding. If either command lacks output, this is a finding.
Discussion
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.
Fix
At a minimum, the audit system should collect unauthorized file accesses for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid=0 -k access -a always,exit -F arch=b32 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid=0 -k access If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid>=500 -F auid!=4294967295 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EACCES -F auid=0 -k access -a always,exit -F arch=b64 -S creat -S open -S openat -S truncate \ -S ftruncate -F exit=-EPERM -F auid=0 -k access
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208906r603263_rule'
OL6-00-000135: All rsyslog-generated log files must have mode 0600 or less permissive.
The file permissions for all log files written by rsyslog should be set to 600, or more restrictive. These log files are determined by the second part of each Rule line in "/etc/rsyslog.conf" and typically all appear in "/var/log". For each log file [LOGFILE] referenced in "/etc/rsyslog.conf", run the following command to inspect the file's permissions: $ ls -l [LOGFILE] The permissions should be 600, or more restrictive. Some log files referenced in /etc/rsyslog.conf may be created by other programs and may require exclusion from consideration. If the permissions are not correct, this is a finding.
Discussion
Log files can contain valuable information regarding system configuration. If the system log files are not protected, unauthorized users could change the logged data, eliminating their forensic value.
Fix
The file permissions for all log files written by rsyslog should be set to 600, or more restrictive. These log files are determined by the second part of each Rule line in "/etc/rsyslog.conf" and typically all appear in "/var/log". For each log file [LOGFILE] referenced in "/etc/rsyslog.conf", run the following command to inspect the file's permissions: $ ls -l [LOGFILE] If the permissions are not 600 or more restrictive, run the following command to correct this: # chmod 0600 [LOGFILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208872r603263_rule'
OL6-00-000198: The audit system must be configured to audit all use of setuid and setgid programs.
To verify that auditing of privileged command use is configured, run the following command once for each local partition [PART] to find relevant setuid / setgid programs: $ sudo find [PART] -xdev -type f -perm /6000 2>/dev/null Run the following command to verify entries in the audit rules for all programs found with the previous command: $ sudo grep path /etc/audit/audit.rules It should be the case that all relevant setuid / setgid programs have a line in the audit rules. If that is not the case, this is a finding.
Discussion
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity.
Fix
At a minimum, the audit system should collect the execution of privileged commands for all users and root. To find the relevant setuid / setgid programs, run the following command for each local partition [PART]: $ sudo find [PART] -xdev -type f -perm /6000 2>/dev/null Then, for each setuid / setgid program on the system, add a line of the following form to "/etc/audit/audit.rules", where [SETUID_PROG_PATH] is the full path to each setuid / setgid program in the list: -a always,exit -F path=[SETUID_PROG_PATH] -F perm=x -F auid>=500 -F auid!=4294967295 -k privileged
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219556r603263_rule'
OL6-00-000268: The rdisc service must not be running.
To check that the "rdisc" service is disabled in system boot configuration, run the following command: # chkconfig "rdisc" --list Output should indicate the "rdisc" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "rdisc" --list "rdisc" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "rdisc" is disabled through current runtime configuration: # service rdisc status If the service is disabled the command will return the following output: rdisc is stopped If the service is running, this is a finding.
Discussion
General-purpose systems typically have their network and routing information configured statically by a system administrator. Workstations or some special-purpose systems often use DHCP (instead of IRDP) to retrieve dynamic network configuration information.
Fix
The "rdisc" service implements the client side of the ICMP Internet Router Discovery Protocol (IRDP), which allows discovery of routers on the local subnet. If a router is discovered then the local routing table is updated with a corresponding default route. By default this daemon is disabled. The "rdisc" service can be disabled with the following commands: # chkconfig rdisc off # service rdisc stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208942r603263_rule'
OL6-00-000148: The operating system must employ automated mechanisms to facilitate the monitoring and control of remote access methods.
Run the following command to determine the current status of the "auditd" service: # service auditd status If the service is enabled, it should return the following: auditd is running... If the service is not running, this is a finding.
Discussion
Ensuring the "auditd" service is active ensures audit records generated by the kernel can be written to disk, or that appropriate actions will be taken if other obstacles exist.
Fix
The "auditd" service is an essential userspace component of the Linux Auditing System, as it is responsible for writing audit records to disk. The "auditd" service can be enabled with the following commands: # chkconfig auditd on # service auditd start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208876r603263_rule'
OL6-00-000260: The system must display a publicly-viewable pattern during a graphical desktop environment session lock.
If the GConf2 package is not installed, this is not applicable. To ensure the screensaver is configured to be blank, run the following command: $ gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gnome-screensaver/mode If properly configured, the output should be "blank-only". If it is not, this is a finding.
Discussion
Setting the screensaver mode to blank-only conceals the contents of the display from passersby.
Fix
Run the following command to set the screensaver mode in the GNOME desktop to a blank screen: # gconftool-2 \ --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type string \ --set /apps/gnome-screensaver/mode blank-only
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208936r603263_rule'
OL6-00-000043: The /etc/group file must be group-owned by root.
To check the group ownership of "/etc/group", run the command: $ ls -l /etc/group If properly configured, the output should indicate the following group-owner. "root" If it does not, this is a finding.
Discussion
The "/etc/group" file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
Fix
To properly set the group owner of "/etc/group", run the command: # chgrp root /etc/group
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208820r603263_rule'
OL6-00-000177: The operating system must automatically audit account termination.
To determine if the system is configured to audit account changes, run the following command: $sudo egrep -w '(/etc/passwd|/etc/shadow|/etc/group|/etc/gshadow|/etc/security/opasswd)' /etc/audit/audit.rules If the system is configured to watch for account changes, lines should be returned for each file specified (and with "-p wa" for each). If the system is not configured to audit account changes, this is a finding.
Discussion
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
Fix
Add the following to "/etc/audit/audit.rules", in order to capture events that modify account changes: # audit_account_changes -w /etc/group -p wa -k audit_account_changes -w /etc/passwd -p wa -k audit_account_changes -w /etc/gshadow -p wa -k audit_account_changes -w /etc/shadow -p wa -k audit_account_changes -w /etc/security/opasswd -p wa -k audit_account_changes
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208890r603263_rule'
OL6-00-000531: The Oracle Linux operating system must mount /dev/shm with the nosuid option.
Verify that the "nosuid" option is configured for /dev/shm. Check that the operating system is configured to use the "nosuid" option for /dev/shm with the following command: # cat /etc/fstab | grep /dev/shm | grep nosuid tmpfs /dev/shm tmpfs defaults,nodev,nosuid,noexec 0 0 If the "nosuid" option is not present on the line for "/dev/shm", this is a finding. Verify "/dev/shm" is mounted with the "nosuid" option: # mount | grep "/dev/shm" | grep nosuid If no results are returned, this is a finding.
Discussion
The "nosuid" mount option causes the system to not execute "setuid" and "setgid" files with owner privileges. This option must be used for mounting any file system not containing approved "setuid" and "setguid" files. Executing files from untrusted file systems increases the opportunity for unprivileged users to attain unauthorized administrative access.
Fix
Configure the "/etc/fstab" to use the "nosuid" option for all lines containing "/dev/shm".
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209074r603263_rule'
OL6-00-000309: The NFS server must not have the insecure file locking option enabled.
To verify insecure file locking has been disabled, run the following command: # grep insecure_locks /etc/exports If there is output, this is a finding.
Discussion
Allowing insecure file locking could allow for sensitive data to be viewed or edited by an unauthorized user.
Fix
By default the NFS server requires secure file-lock requests, which require credentials from the client in order to lock a file. Most NFS clients send credentials with file lock requests, however, there are a few clients that do not send credentials when requesting a file-lock, allowing the client to only be able to lock world-readable files. To get around this, the "insecure_locks" option can be used so these clients can access the desired export. This poses a security risk by potentially allowing the client access to data for which it does not have authorization. Remove any instances of the "insecure_locks" option from the file "/etc/exports".
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-209031r603263_rule'
OL6-00-000298: Emergency accounts must be provisioned with an expiration date.
For every emergency account, run the following command to obtain its account aging and expiration information: # chage -l [USER] Verify each of these accounts has an expiration date set as documented. If any emergency accounts have no expiration date set or do not expire within a documented time frame, this is a finding.
Discussion
When emergency accounts are created, there is a risk they may remain in place and active after the need for them no longer exists. Account expiration greatly reduces the risk of accounts being misused or hijacked.
Fix
In the event emergency accounts are required, configure the system to terminate them after a documented time period. For every emergency account, run the following command to set an expiration date on it, substituting "[USER]" and "[YYYY-MM-DD]" appropriately: # chage -E [YYYY-MM-DD] [USER] "[YYYY-MM-DD]" indicates the documented expiration date for the account.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209028r603263_rule'
OL6-00-000093: The system must ignore ICMPv4 bogus error responses.
The status of the "net.ipv4.icmp_ignore_bogus_error_responses" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.icmp_ignore_bogus_error_responses The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.icmp_ignore_bogus_error_responses /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Ignoring bogus ICMP error responses reduces log size, although some activity would not be logged.
Fix
To set the runtime status of the "net.ipv4.icmp_ignore_bogus_error_responses" kernel parameter, run the following command: # sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.icmp_ignore_bogus_error_responses = 1
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208861r603263_rule'
OL6-00-000047: All system command files must have mode 755 or less permissive.
System executables are stored in the following directories by default: /bin /usr/bin /usr/local/bin /sbin /usr/sbin /usr/local/sbin All files in these directories should not be group-writable or world-writable. To find system executables that are group-writable or world-writable, run the following command for each directory [DIR] which contains system executables: $ find -L [DIR] -perm /022 -type f If any system executables are found to be group-writable or world-writable, this is a finding.
Discussion
System binaries are executed by privileged users, as well as system services, and restrictive permissions are necessary to ensure execution of these programs cannot be co-opted.
Fix
System executables are stored in the following directories by default: /bin /usr/bin /usr/local/bin /sbin /usr/sbin /usr/local/sbin If any file in these directories is found to be group-writable or world-writable, correct its permission with the following command: # chmod go-w [FILE]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208824r603263_rule'
OL6-00-000257: The graphical desktop environment must set the idle timeout to no more than 15 minutes.
If the GConf2 package is not installed, this is not applicable. To check the current idle time-out value, run the following command: $ gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --get /apps/gnome-screensaver/idle_delay If properly configured, the output should be "15". If it is not, this is a finding.
Discussion
Setting the idle delay controls when the screensaver will start, and can be combined with screen locking to prevent access from passersby.
Fix
Run the following command to set the idle time-out value for inactivity in the GNOME desktop to 15 minutes: # gconftool-2 \ --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \ --type int \ --set /apps/gnome-screensaver/idle_delay 15
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208933r603263_rule'
OL6-00-000007: The system must use a separate file system for user home directories.
Run the following command to determine if "/home" is on its own partition or logical volume: $ mount | grep "on /home " If "/home" has its own partition or volume group, a line will be returned. If no line is returned, this is a finding.
Discussion
Ensuring that "/home" is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.
Fix
If user home directories will be stored locally, create a separate partition for "/home" at installation time (or migrate it later using LVM). If "/home" will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208796r603263_rule'
OL6-00-000185: The audit system must be configured to audit all discretionary access control permission modifications using chown.
To determine if the system is configured to audit calls to the "chown" system call, run the following command: $ sudo grep -w "chown" /etc/audit/audit.rules -a always,exit -F arch=b32 -S chown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S chown -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S chown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S chown -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "chown" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S chown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S chown -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S chown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S chown -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208894r603263_rule'
OL6-00-000296: All accounts on the system must have unique user or account names.
Run the following command to check for duplicate account names: # pwck -rq If there are no duplicate names, no line will be returned. If a line is returned, this is a finding.
Discussion
Unique usernames allow for accountability on the system.
Fix
Change usernames, or delete accounts, so each has a unique name.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209026r603263_rule'
OL6-00-000124: The Datagram Congestion Control Protocol (DCCP) must be disabled unless required.
If the system is configured to prevent the loading of the "dccp" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": grep -r dccp /etc/modprobe.conf /etc/modprobe.d | grep -i “/bin/true” If no line is returned, this is a finding.
Discussion
Disabling DCCP protects the system against exploitation of any flaws in its implementation.
Fix
The Datagram Congestion Control Protocol (DCCP) is a relatively new transport layer protocol, designed to support streaming media and telephony. To configure the system to prevent the "dccp" kernel module from being loaded, add the following line to a file in the directory "/etc/modprobe.d": install dccp /bin/true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208866r603263_rule'
OL6-00-000057: The system must require passwords to contain at least one uppercase alphabetic character.
To check how many uppercase characters are required in a password, run the following command: $ grep pam_cracklib /etc/pam.d/system-auth /etc/pam.d/password-auth The "ucredit" parameter (as a negative number) will indicate how many uppercase characters are required. The DoD requires at least one uppercase character in a password. This would appear as "ucredit=-1". If the “ucredit” parameter is not found or not set to the required value, this is a finding.
Discussion
Requiring a minimum number of uppercase characters makes password guessing attacks more difficult by ensuring a larger search space.
Fix
The pam_cracklib module's "ucredit=" parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_cracklib will grant +1 additional length credit for each uppercase character. Edit /etc/pam.d/system-auth and /etc/pam.d/password-auth adding "ucredit=-1" after pam_cracklib.so to require use of an uppercase character in passwords.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208832r603263_rule'
OL6-00-000196: The audit system must be configured to audit all discretionary access control permission modifications using setxattr.
To determine if the system is configured to audit calls to the "setxattr" system call, run the following command: $ sudo grep -w "setxattr" /etc/audit/audit.rules -a always,exit -F arch=b32 -S setxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S setxattr -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S setxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S setxattr -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "setxattr" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S setxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S setxattr -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S setxattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S setxattr -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208905r603263_rule'
OL6-00-000273: The system must use SMB client signing for connecting to samba servers using mount.cifs.
If Samba is not in use, this is not applicable. To verify that Samba clients using mount.cifs must use packet signing, run the following command: # grep sec /etc/fstab /etc/mtab The output should show either "krb5i" or "ntlmv2i" in use. If it does not, this is a finding.
Discussion
Packet signing can prevent man-in-the-middle attacks which modify SMB packets in transit.
Fix
Require packet signing of clients who mount Samba shares using the "mount.cifs" program (e.g., those who specify shares in "/etc/fstab"). To do so, ensure signing options (either "sec=krb5i" or "sec=ntlmv2i") are used. See the "mount.cifs(8)" man page for more information. A Samba client should only communicate with servers who can support SMB packet signing.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209011r603263_rule'
OL6-00-000137: The operating system must support the requirement to centrally manage the content of audit records generated by organization defined information system components.
To ensure logs are sent to a remote host, examine the file "/etc/rsyslog.conf". If using UDP, a line similar to the following should be present: *.* @[loghost.example.com] If using TCP, a line similar to the following should be present: *.* @@[loghost.example.com] If using RELP, a line similar to the following should be present: *.* :omrelp:[loghost.example.com] If none of these are present, this is a finding.
Discussion
A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.
Fix
To configure rsyslog to send logs to a remote log server, open "/etc/rsyslog.conf" and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting "[loghost.example.com]" appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments. To use UDP for log message delivery: *.* @[loghost.example.com] To use TCP for log message delivery: *.* @@[loghost.example.com] To use RELP for log message delivery: *.* :omrelp:[loghost.example.com]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219555r603263_rule'
OL6-00-000083: The system must not accept IPv4 source-routed packets on any interface.
The status of the "net.ipv4.conf.all.accept_source_route" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.accept_source_route The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.all.accept_source_route /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.
Fix
To set the runtime status of the "net.ipv4.conf.all.accept_source_route" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.accept_source_route=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.accept_source_route = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208853r603263_rule'
OL6-00-000081: The system must not send ICMPv4 redirects from any interface.
The status of the "net.ipv4.conf.all.send_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.send_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.all.send_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
Sending ICMP redirects permits the system to instruct other systems to update their routing information. The ability to send ICMP redirects is only appropriate for systems acting as routers.
Fix
To set the runtime status of the "net.ipv4.conf.all.send_redirects" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.send_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.send_redirects = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208851r603263_rule'
OL6-00-000055: System and application account passwords must be changed at least annually.
Obtain a list of approved system and application accounts from the ISSO. For each system and application account identified, run the following command: # chage -l <application_account> Last password change : Nov 05, 2018 Password expires : Nov 04, 2019 Password inactive : Dec 10, 2019 Account expires : never Minimum number of days between password change : 1 Maximum number of days between password change : 365 Number of days of warning before password expires : 7 If "Maximum number of days between password change" is greater than "365", this is a finding. If the date of "Last password change" exceeds 365 days, this is a finding. If the date of "Password expires" is greater than 365 days from the date of "Last password change", this is a finding.
Discussion
Any password, no matter how complex, can eventually be cracked. Therefore, system and application account passwords need to be changed periodically. If an organization fails to change the system and application account passwords at least annually, there is the risk that the account passwords could be compromised.
Fix
Set the "Maximum number of days between password change" to "365": # chage -M 365 <application_account> Change the password for the system/application account: #passwd <application_account>
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208830r603263_rule'
OL6-00-000320: The systems local firewall must implement a deny-all, allow-by-exception policy for forwarded packets.
Run the following command to ensure the default "FORWARD" policy is "DROP": grep ":FORWARD" /etc/sysconfig/iptables The output must be the following: # grep ":FORWARD" /etc/sysconfig/iptables :FORWARD DROP [0:0] If it is not, this is a finding.
Discussion
In "iptables" the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to "DROP" implements proper design for a firewall, i.e., any packets which are not explicitly permitted should not be accepted.
Fix
To set the default policy to DROP (instead of ACCEPT) for the built-in FORWARD chain which processes packets that will be forwarded from one interface to another, add or correct the following line in "/etc/sysconfig/iptables": :FORWARD DROP [0:0]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219579r603263_rule'
OL6-00-000138: System logs must be rotated daily.
Run the following commands to determine the current status of the "logrotate" service: # grep logrotate /var/log/cron* If the logrotate service is not run on a daily basis by cron, this is a finding.
Discussion
Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full.
Fix
The "logrotate" service should be installed or reinstalled if it is not installed and operating properly, by running the following command: # yum reinstall logrotate
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208874r603263_rule'
OL6-00-000529: The sudo command must require authentication.
Verify neither the "NOPASSWD" option nor the "!authenticate" option is configured for use in "/etc/sudoers" and associated files. Note that the "#include" and "#includedir" directives may be used to include configuration data from locations other than the defaults enumerated here. # egrep '^[^#]*NOPASSWD' /etc/sudoers /etc/sudoers.d/* # egrep '^[^#]*!authenticate' /etc/sudoers /etc/sudoers.d/* If any occurrences of "NOPASSWD" or “!authenticate” are returned from these commands and have not been documented with the ISSO as an organizationally defined administrative group utilizing MFA, this is a finding.
Discussion
The "sudo" command allows authorized users to run programs (including shells) as other users, system users, and root. The "/etc/sudoers" file is used to configure authorized "sudo" users as well as the programs they are allowed to run. Some configuration options in the "/etc/sudoers" file allow configured users to run programs without re-authenticating. Use of these configuration options makes it easier for one compromised account to be used to compromise other accounts.
Fix
Update the "/etc/sudoers" or other sudo configuration files to remove or comment out lines utilizing the "NOPASSWD" and "!authenticate" options. # visudo # visudo -f [other sudo configuration file]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209072r603263_rule'
OL6-00-000099: The system must ignore ICMPv6 redirects by default.
If IPv6 is disabled, this is not applicable. The status of the "net.ipv6.conf.default.accept_redirects" kernel parameter can be queried by running the following command: $ sysctl net.ipv6.conf.default.accept_redirects The output of the command should indicate a value of "0". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv6.conf.default.accept_redirects /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
An illicit ICMP redirect message could result in a man-in-the-middle attack.
Fix
To set the runtime status of the "net.ipv6.conf.default.accept_redirects" kernel parameter, run the following command: # sysctl -w net.ipv6.conf.default.accept_redirects=0 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv6.conf.default.accept_redirects = 0
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208865r603263_rule'
OL6-00-000297: Temporary accounts must be provisioned with an expiration date.
For every temporary account, run the following command to obtain its account aging and expiration information: # chage -l [USER] Verify each of these accounts has an expiration date set as documented. If any temporary accounts have no expiration date set or do not expire within a documented time frame, this is a finding.
Discussion
When temporary accounts are created, there is a risk they may remain in place and active after the need for them no longer exists. Account expiration greatly reduces the risk of accounts being misused or hijacked.
Fix
In the event temporary accounts are required, configure the system to terminate them after a documented time period. For every temporary account, run the following command to set an expiration date on it, substituting "[USER]" and "[YYYY-MM-DD]" appropriately: # chage -E [YYYY-MM-DD] [USER] "[YYYY-MM-DD]" indicates the documented expiration date for the account.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209027r603263_rule'
OL6-00-000277: The operating system must employ cryptographic mechanisms to prevent unauthorized disclosure of data at rest unless otherwise protected by alternative physical measures.
Determine if encryption must be used to protect data on the system. If encryption must be used and is not employed, this is a finding.
Discussion
The risk of a system's physical compromise, particularly mobile systems such as laptops, places its data at risk of compromise. Encrypting this data mitigates the risk of its loss if the system is lost.
Fix
The operating system natively supports partition encryption through the Linux Unified Key Setup (LUKS) on-disk-format technology. The easiest way to encrypt a partition is during installation time. For manual installations, select the "Encrypt" checkbox during partition creation to encrypt the partition. When this option is selected, the system will prompt for a passphrase to use in decrypting the partition. The passphrase will subsequently need to be entered manually every time the system boots. For automated/unattended installations, it is possible to use Kickstart by adding the "--encrypted" and "--passphrase=" options to the definition of each partition to be encrypted. For example, the following line would encrypt the root partition: part / --fstype=ext3 --size=100 --onpart=hda1 --encrypted --passphrase=[PASSPHRASE] Any [PASSPHRASE] is stored in the Kickstart in plaintext, and the Kickstart must then be protected accordingly. Omitting the "--passphrase=" option from the partition definition will cause the installer to pause and interactively ask for the passphrase during installation. Detailed information on encrypting partitions using LUKS can be found in the Oracle Linux documentation at: http://docs.oracle.com/cd/E37670_01/E36387/html/index.html. Additional information is available from: http://linux.oracle.com/documentation/OL6/Red_Hat_Enterprise_Linux-6-Security_Guide-en-US.pdf"
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219567r603263_rule'
OL6-00-000171: The audit system must be configured to audit all attempts to alter system time through clock_settime.
To determine if the system is configured to audit calls to the "clock_settime" system call, run the following command: $ sudo grep -w "clock_settime" /etc/audit/audit.rules -a always,exit -F arch=b32 -S clock_settime -k audit_time_rules -a always,exit -F arch=b64 -S clock_settime -k audit_time_rules If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "clock_settime" system call, this is a finding.
Discussion
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
Fix
On a 32-bit system, add the following to "/etc/audit/audit.rules": # audit_time_rules -a always,exit -F arch=b32 -S clock_settime -k audit_time_rules If the system is 64-bit, then also add the following: # audit_time_rules -a always,exit -F arch=b64 -S clock_settime -k audit_time_rules
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208885r603263_rule'
OL6-00-000243: The Oracle Linux 6 operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections.
Only FIPS-approved ciphers should be used. To verify that only FIPS-approved ciphers are in use, run the following command: # grep -i Ciphers /etc/ssh/sshd_config Ciphers aes256-ctr,aes192-ctr,aes128-ctr If any ciphers other than "aes256-ctr", "aes192-ctr", or "aes128-ctr" are listed, the order differs from the example above, the "Ciphers" keyword is missing, or the returned line is commented out, this is a finding.
Discussion
Approved algorithms should impart some level of confidence in their implementation. These are also required for compliance. The system will attempt to use the first cipher presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest cipher available to secure the SSH connection.
Fix
Limit the ciphers to those algorithms which are FIPS-approved. The following line in "/etc/ssh/sshd_config" demonstrates use of FIPS-approved ciphers: Ciphers 256-ctr,aes192-ctr,aes128-ctr Note: The man page "sshd_config(5)" contains a list of supported ciphers.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219561r744067_rule'
OL6-00-000308: Process core dumps must be disabled unless needed.
To verify that core dumps are disabled for all users, run the following command: $ grep core /etc/security/limits.conf /etc/security/limits.d/*.conf The output should be: * hard core 0 If it is not, this is a finding.
Discussion
A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers trying to debug problems.
Fix
To disable core dumps for all users, add the following line to "/etc/security/limits.conf": * hard core 0
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209030r603263_rule'
OL6-00-000037: The /etc/gshadow file must be group-owned by root.
To check the group ownership of "/etc/gshadow", run the command: $ ls -l /etc/gshadow If properly configured, the output should indicate the following group-owner. "root" If it does not, this is a finding.
Discussion
The "/etc/gshadow" file contains group password hashes. Protection of this file is critical for system security.
Fix
To properly set the group owner of "/etc/gshadow", run the command: # chgrp root /etc/gshadow
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208814r603263_rule'
OL6-00-000266: The oddjobd service must not be running.
To check that the "oddjobd" service is disabled in system boot configuration, run the following command: # chkconfig "oddjobd" --list Output should indicate the "oddjobd" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "oddjobd" --list "oddjobd" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "oddjobd" is disabled through current runtime configuration: # service oddjobd status If the service is disabled the command will return the following output: oddjobd is stopped If the service is running, this is a finding.
Discussion
The "oddjobd" service may provide necessary functionality in some environments but it can be disabled if it is not needed. Execution of tasks by privileged programs, on behalf of unprivileged ones, has traditionally been a source of privilege escalation security issues.
Fix
The "oddjobd" service exists to provide an interface and access control mechanism through which specified privileged tasks can run tasks for unprivileged client applications. Communication with "oddjobd" is through the system message bus. The "oddjobd" service can be disabled with the following commands: # chkconfig oddjobd off # service oddjobd stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208940r603263_rule'
OL6-00-000029: Default operating system accounts, other than root, must be locked.
To obtain a listing of all users and the contents of their shadow password field, run the command: $ awk -F: '$1 !~ /^root$/ && $2 !~ /^[!*]/ {print $1 ":" $2}' /etc/shadow Identify the operating system accounts from this listing. These will primarily be the accounts with UID numbers less than 500, other than root. If any default operating system account (other than root) has a valid password hash, this is a finding.
Discussion
Disabling authentication for default system accounts makes it more difficult for attackers to make use of them to compromise a system.
Fix
Some accounts are not associated with a human user of the system, and exist to perform some administrative function. An attacker should not be able to log into these accounts. Disable logon access to these accounts with the command: # passwd -l [SYSACCT]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208806r603263_rule'
OL6-00-000203: The xinetd service must be disabled if no network services utilizing it are enabled.
If network services are using the xinetd service, this is not applicable. To check that the "xinetd" service is disabled in system boot configuration, run the following command: # chkconfig "xinetd" --list Output should indicate the "xinetd" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "xinetd" --list "xinetd" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "xinetd" is disabled through current runtime configuration: # service xinetd status If the service is disabled the command will return the following output: xinetd is stopped If the service is running, this is a finding.
Discussion
The xinetd service provides a dedicated listener service for some programs, which is no longer necessary for commonly-used network services. Disabling it ensures that these uncommon services are not running, and also prevents attacks against xinetd itself.
Fix
The "xinetd" service can be disabled with the following commands: # chkconfig xinetd off # service xinetd stop
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208911r603263_rule'
OL6-00-000056: The system must require passwords to contain at least one numeric character.
To check how many digits are required in a password, run the following command: $ grep pam_cracklib /etc/pam.d/system-auth /etc/pam.d/password-auth The "dcredit" parameter (as a negative number) will indicate how many digits are required. The DoD requires at least one digit in a password. This would appear as "dcredit=-1". If the “dcredit” parameter is not found or not set to the required value, this is a finding.
Discussion
Requiring digits makes password guessing attacks more difficult by ensuring a larger search space.
Fix
The pam_cracklib module's "dcredit" parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_cracklib will grant +1 additional length credit for each digit. Edit /etc/pam.d/system-auth and /etc/pam.d/password-auth adding "dcredit=-1" after pam_cracklib.so to require use of a digit in passwords.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208831r603263_rule'
OL6-00-000537: The Oracle Linux operating system must require re-authentication when using the "sudo" command.
Verify the operating system requires re-authentication when using the "sudo" command to elevate privileges. $ sudo grep -i 'timestamp_timeout' /etc/sudoers /etc/sudoers.d/* /etc/sudoers:Defaults timestamp_timeout=0 If "timestamp_timeout" is set to a negative number, is commented out, or no results are returned, this is a finding.
Discussion
Without re-authentication, users may access resources or perform tasks for which they do not have authorization. When operating systems provide the capability to escalate a functional capability, it is critical the organization requires the user to re-authenticate when using the "sudo" command. If the value is set to an integer less than 0, the user's time stamp will not expire and the user will not have to re-authenticate for privileged actions until the user's session is terminated.
Fix
Configure the "sudo" command to require re-authentication. Edit the /etc/sudoers file: $ sudo visudo Add or modify the following line: Defaults timestamp_timeout=[value] Note: The "[value]" must be a number that is greater than or equal to "0".
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
None
OL6-00-000032: The root account must be the only account having a UID of 0.
To list all password file entries for accounts with UID 0, run the following command: # awk -F: '($3 == 0) {print}' /etc/passwd This should print only one line, for the user root. If any account other than root has a UID of 0, this is a finding.
Discussion
An account has root authority if it has a UID of 0. Multiple accounts with a UID of 0 afford more opportunity for potential intruders to guess a password for a privileged account. Proper configuration of sudo is recommended to afford multiple system administrators access to root privileges in an accountable manner.
Fix
If any account other than root has a UID of 0, this misconfiguration should be investigated and the accounts other than root should be removed or have their UID changed.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208809r603263_rule'
OL6-00-000060: The system must require at least eight characters be changed between the old and new passwords during a password change.
To check how many characters must differ during a password change, run the following command: $ grep pam_cracklib /etc/pam.d/system-auth /etc/pam.d/password-auth The "difok" parameter will indicate how many characters must differ. The DoD requires eight characters differ during a password change. This would appear as "difok=8". If the “difok” parameter is not found or not set to the required value, this is a finding.
Discussion
Requiring a minimum number of different characters during password changes ensures that newly changed passwords should not resemble previously compromised ones. Note: Passwords which are changed on compromised systems will still be compromised.
Fix
The pam_cracklib module's "difok" parameter controls requirements for usage of different characters during a password change. Edit /etc/pam.d/system-auth and /etc/pam.d/password-auth adding "difok=[NUM]" after pam_cracklib.so to require differing characters when changing passwords, substituting [NUM] appropriately. The DoD requirement is “8”.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208835r603263_rule'
OL6-00-000519: The system package management tool must verify contents of all files associated with packages.
The following command will list which files on the system have file hashes different from what is expected by the RPM database. # rpm -Va | awk '$1 ~ /..5/ && $2 != "c"' If any output is produced, verify that the changes were due to STIG application and have been documented with the ISSO. If any output has not been documented with the ISSO, this is a finding.
Discussion
The hash on important files like system executables should match the information given by the RPM database. Executables with erroneous hashes could be a sign of nefarious activity on the system.
Fix
The RPM package management system can check the hashes of installed software packages, including many that are important to system security. Run the following command to list which files on the system have hashes that differ from what is expected by the RPM database: # rpm -Va | grep '^..5' A "c" in the second column indicates that a file is a configuration file, which may appropriately be expected to change. If the file that has changed was not expected to then refresh from distribution media or online repositories. rpm -Uvh [affected_package] OR yum reinstall [affected_package]
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209064r603263_rule'
OL6-00-000340: The snmpd service must use only SNMP protocol version 3 or newer.
To ensure only SNMPv3 or newer is used, run the following command: # grep 'v1\|v2c\|com2sec' /etc/snmp/snmpd.conf | grep -v '^#' There should be no output. If there is output, this is a finding.
Discussion
Earlier versions of SNMP are considered insecure, as they potentially allow unauthorized access to detailed system management information.
Fix
Edit "/etc/snmp/snmpd.conf", removing any references to "v1", "v2c", or "com2sec". Upon doing that, restart the SNMP service: # service snmpd restart
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209042r603263_rule'
OL6-00-000117: The operating system must prevent public IPv4 access into an organizations internal networks, except as appropriately mediated by managed interfaces employing boundary protection devices.
If the system is a cross-domain system, this is not applicable. Run the following command to determine the current status of the "iptables" service: # service iptables status If the service is not running, it should return the following: iptables: Firewall is not running. If the service is not running, this is a finding.
Discussion
The "iptables" service provides the system's host-based firewalling capability for IPv4 and ICMP.
Fix
The "iptables" service can be enabled with the following commands: # chkconfig iptables on # service iptables start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219553r603263_rule'
OL6-00-000338: The TFTP daemon must operate in secure mode which provides access only to a single directory on the host file system.
Verify the "tftp" package is installed: # rpm -qa | grep -i tftp tftp-5.2-22.e16.x86_64 If the "tftp" package is not installed, this is Not Applicable. Verify "tftp" is configured by with the "-s" option by running the following command: grep "server_args" /etc/xinetd.d/tftp The output should indicate the "server_args" variable is configured with the "-s" flag, matching the example below: # grep "server_args" /etc/xinetd.d/tftp server_args = -s /var/lib/tftpboot If it does not, this is a finding.
Discussion
Using the "-s" option causes the TFTP service to only serve files from the given directory. Serving files from an intentionally specified directory reduces the risk of sharing files which should remain private.
Fix
If running the "tftp" service is necessary, it should be configured to change its root directory at startup. To do so, ensure "/etc/xinetd.d/tftp" includes "-s" as a command line argument, as shown in the following example (which is also the default): server_args = -s /var/lib/tftpboot
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-209040r603263_rule'
OL6-00-000163: The audit system must switch the system to single-user mode when available audit storage volume becomes dangerously low.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine if the system is configured to either suspend, switch to single-user mode, or halt when disk space has run low: admin_space_left_action = single If the system is not configured to switch to single-user mode, suspend, or halt for corrective action, this is a finding.
Discussion
Administrators should be made aware of an inability to record audit records. If a separate partition or logical volume of adequate size is used, running low on space for audit records should never occur.
Fix
The "auditd" service can be configured to take an action when disk space is running low but prior to running out of space completely. Edit the file "/etc/audit/auditd.conf". Add or modify the following line, substituting [ACTION] appropriately: admin_space_left_action = [ACTION] Set this value to "single" to cause the system to switch to single-user mode for corrective action. Acceptable values also include "suspend" and "halt". For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for [ACTION] are described in the "auditd.conf" man page.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208881r603263_rule'
OL6-00-000079: The system must limit the ability of processes to have simultaneous write and execute access to memory.
If the system being evaluated is running a Red Hat-compatible operating system kernel, check that the "kernel.exec-shield" kernel parameter is set to "1" in /etc/sysctl.conf. If the system is running an Oracle Unbreakable Enterprise kernel, verify that Oracle's Data Execution Prevention is enabled. First, determine if the system is operating an Oracle Unbreakable Enterprise Kernel (UEK): # uname -r | grep uek If no value is returned, the system is running a Red Hat-compatible kernel. Verify that the "kernel.exec-shield" kernel parameter is set to "1" in the running kernel and /etc/sysctl.conf: # sysctl kernel.exec-shield # grep ^kernel\.exec-shield /etc/sysctl.conf | awk -F= '{ print $2 }' kernel.exec-shield = 1 If there is no value returned, or if a value is returned that is not "1", this is a finding. If the system was found to be running an Unbreakable Enterprise Kernel, verify that DEP is enabled: # dmesg | grep 'NX.*protection:' If there is no value returned, or if a value is returned that is not "NX (Execute Disable) protection: active", this is a finding. Note that this is not a finding when the underlying processor architecture does not support the "Execute Disable" (NX) capability. To determine if the processor supports the NX capability, run the following: # grep nx /proc/cpuinfo If there is no value returned, this is not applicable.
Discussion
A common type of exploit is the stack buffer overflow. An application receives from an attacker more data than it is prepared for and stores this information on its stack, writing beyond the space reserved for it. This can be designed to cause execution of the data written on the stack. One mechanism to mitigate this vulnerability is for the system to not allow the execution of instructions in sections of memory identified as part of the stack.
Fix
If the system being evaluated is running a Red Hat-compatible operating system kernel, then ensure that the "kernel.exec-shield" kernel parameter is set to "1". If the system is running an Oracle Unbreakable Enterprise Kernel, this parameter does not exist. When an Unbreakable Enterprise Kernel is booted, Oracle's Data Execution Prevention (DEP) feature will leverage the hardware-enforced NX (never execute) bit of compatible CPUs to protect against code being executed from the stack. By default, DEP is enabled. If DEP is not enabled, ensure that the string "noexec=off" does not appear in /boot/grub/grub.conf. First, determine if the system is operating an Oracle Unbreakable Enterprise Kernel (UEK): # uname -r | grep uek If no value is returned, the system is running a Red Hat-compatible kernel. Edit (or add if necessary) the entry in /etc/sysctl.conf for the "kernel.exec-shield" kernel parameter. Ensure that this parameter is set to "1" as in: kernel.exec-shield = 1 If this was not already the default, reboot the system for the change to take effect. If the system was found to be running an Unbreakable Enterprise Kernel, then ensure that the string "noexec=off" is not found in /boot/grub/grub.conf: # grep noexec=off /boot/grub/grub.conf If found, remove the offending kernels from /boot/grub/grub.conf.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208849r603263_rule'
OL6-00-000193: The audit system must be configured to audit all discretionary access control permission modifications using lremovexattr.
To determine if the system is configured to audit calls to the "lremovexattr" system call, run the following command: $ sudo grep -w "lremovexattr" /etc/audit/audit.rules -a always,exit -F arch=b32 -S lremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S lremovexattr -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S lremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S lremovexattr -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "lremovexattr" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S lremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S lremovexattr -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S lremovexattr -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S lremovexattr -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208902r603263_rule'
OL6-00-000269: Remote file systems must be mounted with the nodev option.
To verify the "nodev" option is configured for all NFS mounts, run the following command: $ mount | grep nfs All NFS mounts should show the "nodev" setting in parentheses, along with other mount options. If the setting does not show, this is a finding.
Discussion
Legitimate device files should only exist in the /dev directory. NFS mounts should not present device files to users.
Fix
Add the "nodev" option to the fourth column of "/etc/fstab" for the line which controls mounting of any NFS mounts.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209008r603263_rule'
OL6-00-000348: The FTPS/FTP service on the system must be configured with the Department of Defense (DoD) login banner.
Verify the "vsftpd" package is installed: # rpm -qa | grep -i vsftpd vsftpd-3.0.2-22.e16.x86_64 If the "vsftpd" package is not installed, this is Not Applicable. To verify this configuration, run the following command: grep "banner_file" /etc/vsftpd/vsftpd.conf The output should show the value of "banner_file" is set to "/etc/issue", an example of which is shown below. # grep "banner_file" /etc/vsftpd/vsftpd.conf banner_file=/etc/issue If it does not, this is a finding.
Discussion
This setting will cause the system greeting banner to be used for FTP connections as well.
Fix
Edit the vsftpd configuration file, which resides at "/etc/vsftpd/vsftpd.conf" by default. Add or correct the following configuration options. banner_file=/etc/issue Restart the vsftpd daemon. # service vsftpd restart
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209050r603263_rule'
OL6-00-000095: The system must be configured to use TCP syncookies when experiencing a TCP SYN flood.
The status of the "net.ipv4.tcp_syncookies" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.tcp_syncookies The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.tcp_syncookies /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests.
Fix
To set the runtime status of the "net.ipv4.tcp_syncookies" kernel parameter, run the following command: # sysctl -w net.ipv4.tcp_syncookies=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.tcp_syncookies = 1
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208862r603263_rule'
OL6-00-000017: The system must use a Linux Security Module at boot time.
Inspect "/boot/grub/grub.conf" for any instances of "selinux=0" in the kernel boot arguments. Presence of "selinux=0" indicates that SELinux is disabled at boot time. If SELinux is disabled at boot time, this is a finding.
Discussion
Disabling a major host protection feature, such as SELinux, at boot time prevents it from confining system services at boot time. Further, it increases the chances that it will remain off during system operation.
Fix
SELinux can be disabled at boot time by an argument in "/boot/grub/grub.conf". Remove any instances of "selinux=0" from the kernel arguments in that file to prevent SELinux from being disabled at boot.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208799r603263_rule'
OL6-00-000036: The /etc/gshadow file must be owned by root.
To check the ownership of "/etc/gshadow", run the command: $ ls -l /etc/gshadow If properly configured, the output should indicate the following owner: "root" If it does not, this is a finding.
Discussion
The "/etc/gshadow" file contains group password hashes. Protection of this file is critical for system security.
Fix
To properly set the owner of "/etc/gshadow", run the command: # chown root /etc/gshadow
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208813r603263_rule'
OL6-00-000505: The operating system must conduct backups of system-level information contained in the information system per organization defined frequency to conduct backups that are consistent with recovery time and recovery point objectives.
Ask an administrator if a process exists to back up OS data from the system, including configuration data. If such a process does not exist, this is a finding.
Discussion
Operating system backup is a critical step in maintaining data assurance and availability. System-level information includes system-state information, operating system and application software, and licenses. Backups must be consistent with organizational recovery time and recovery point objectives.
Fix
Procedures to back up operating system data from the system must be established and executed. The operating system provides utilities for automating such a process. Commercial and open-source products are also available. Implement a process whereby OS data is backed up from the system in accordance with local policies.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219586r603263_rule'
OL6-00-000062: The system must use a FIPS 140-2-approved cryptographic hashing algorithm for generating account password hashes (system-auth).
Inspect the "password" section of "/etc/pam.d/system-auth", "/etc/pam.d/system-auth-ac", "/etc/pam.d/password-auth", "/etc/pam.d/password-auth-ac", and other files in "/etc/pam.d" to identify the number of occurrences where the “pam_unix.so” module is used in the “password” section. $ grep -E -c 'password.*pam_unix.so' /etc/pam.d/* /etc/pam.d/atd:0 /etc/pam.d/config-util:0 /etc/pam.d/crond:0 /etc/pam.d/login:0 /etc/pam.d/other:0 /etc/pam.d/passwd:0 /etc/pam.d/password-auth:1 /etc/pam.d/password-auth-ac:1 /etc/pam.d/sshd:0 /etc/pam.d/su:0 /etc/pam.d/sudo:0 /etc/pam.d/system-auth:1 /etc/pam.d/system-auth-ac:1 /etc/pam.d/vlock:0 Note: The number adjacent to the file name indicates how many occurrences of the “pam_unix.so” module are found in the password section. If the “pam_unix.so” module is not defined in the “password” section of “/etc/pam.d/system-auth”, “/etc/pam.d/system-auth-ac”, “/etc/pam.d/password-auth”, and “/etc/pam.d/password-auth-ac” at a minimum, this is a finding. Verify that the “sha512” variable is used with each instance of the “pam_unix.so” module in the “password” section: $ grep password /etc/pam.d/* | grep pam_unix.so | grep sha512 /etc/pam.d/password-auth:password sufficient pam_unix.so sha512 [other arguments…] /etc/pam.d/password-auth-ac:password sufficient pam_unix.so sha512 [other arguments…] /etc/pam.d/system-auth:password sufficient pam_unix.so sha512 [other arguments…] /etc/pam.d/system-auth-ac:password sufficient pam_unix.so sha512 [other arguments…] If this list of files does not coincide with the previous command, this is a finding. If any of the identified “pam_unix.so” modules do not use the “sha512” variable, this is a finding.
Discussion
Using a stronger hashing algorithm makes password-cracking attacks more difficult.
Fix
In "/etc/pam.d/system-auth”, "/etc/pam.d/system-auth-ac", “/etc/pam.d/password-auth”, and “/etc/pam.d/password-auth-ac”, among potentially other files, the "password" section of the files control which PAM modules execute during a password change. Set the "pam_unix.so" module in the "password" section to include the argument "sha512", as shown below: password sufficient pam_unix.so sha512 [other arguments...] This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default. Note: Any updates made to "/etc/pam.d/system-auth" and "/etc/pam.d/password-auth" will be overwritten by the "authconfig" program. The "authconfig" program should not be used.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208837r603263_rule'
OL6-00-000528: The noexec option must be added to the /tmp partition.
To verify that binaries cannot be directly executed from the /tmp directory, run the following command: $ grep '\s/tmp' /etc/fstab The resulting output will show whether the /tmp partition has the "noexec" flag set. If the /tmp partition does not have the noexec flag set, this is a finding.
Discussion
Allowing users to execute binaries from world-writable directories such as "/tmp" should never be necessary in normal operation and can expose the system to potential compromise.
Fix
The "noexec" mount option can be used to prevent binaries from being executed out of "/tmp". Add the "noexec" option to the fourth column of "/etc/fstab" for the line which controls mounting of "/tmp".
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209071r603263_rule'
OL6-00-000285: The Oracle Linux operating system must implement the Endpoint Security for Linux Threat Prevention tool.
Per OPORD 16-0080, the preferred endpoint security tool is McAfee Endpoint Security for Linux (ENSL) in conjunction with SELinux. Procedure: Check that the following package has been installed: # rpm -qa | grep -i mcafeetp If the "mcafeetp" package is not installed, this is a finding. Verify that the daemon is running: # ps -ef | grep -i mfetpd If the daemon is not running, this is a finding.
Discussion
Adding endpoint security tools can provide the capability to automatically take actions in response to malicious behavior, which can provide additional agility in reacting to network threats. These tools also often include a reporting capability to provide network awareness of system, which may not otherwise exist in an organization's systems management regime.
Fix
Install and enable the latest McAfee ENSLTP package.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
None
OL6-00-000088: The system must log Martian packets.
The status of the "net.ipv4.conf.all.log_martians" kernel parameter can be queried by running the following command: $ sysctl net.ipv4.conf.all.log_martians The output of the command should indicate a value of "1". If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". $ grep net.ipv4.conf.all.log_martians /etc/sysctl.conf If the correct value is not returned, this is a finding.
Discussion
The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected.
Fix
To set the runtime status of the "net.ipv4.conf.all.log_martians" kernel parameter, run the following command: # sysctl -w net.ipv4.conf.all.log_martians=1 If this is not the system's default value, add the following line to "/etc/sysctl.conf": net.ipv4.conf.all.log_martians = 1
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208856r603263_rule'
OL6-00-000069: The system must require authentication upon booting into single-user and maintenance modes.
To check if authentication is required for single-user mode, run the following command: $ grep SINGLE /etc/sysconfig/init The output should be the following: SINGLE=/sbin/sulogin If the output is different, this is a finding.
Discussion
This prevents attackers with physical access from trivially bypassing security on the machine and gaining root access. Such accesses are further prevented by configuring the bootloader password.
Fix
Single-user mode is intended as a system recovery method, providing a single user root access to the system by providing a boot option at startup. By default, no authentication is performed if single-user mode is selected. To require entry of the root password even if the system is started in single-user mode, add or correct the following line in the file "/etc/sysconfig/init": SINGLE=/sbin/sulogin
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208844r603263_rule'
OL6-00-000175: The operating system must automatically audit account modification.
To determine if the system is configured to audit account changes, run the following command: $sudo egrep -w '(/etc/passwd|/etc/shadow|/etc/group|/etc/gshadow|/etc/security/opasswd)' /etc/audit/audit.rules If the system is configured to watch for account changes, lines should be returned for each file specified (and with "-p wa" for each). If the system is not configured to audit account changes, this is a finding.
Discussion
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
Fix
Add the following to "/etc/audit/audit.rules", in order to capture events that modify account changes: # audit_account_changes -w /etc/group -p wa -k audit_account_changes -w /etc/passwd -p wa -k audit_account_changes -w /etc/gshadow -p wa -k audit_account_changes -w /etc/shadow -p wa -k audit_account_changes -w /etc/security/opasswd -p wa -k audit_account_changes
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208888r603263_rule'
OL6-00-000167: The audit system must be configured to audit all attempts to alter system time through settimeofday.
To determine if the system is configured to audit calls to the "settimeofday" system call, run the following command: $ sudo grep -w "settimeofday" /etc/audit/audit.rules -a always,exit -F arch=b32 -S settimeofday -k audit_time_rules -a always,exit -F arch=b64 -S settimeofday -k audit_time_rules If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "settimeofday" system call, this is a finding.
Discussion
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
Fix
On a 32-bit system, add the following to "/etc/audit/audit.rules": # audit_time_rules -a always,exit -F arch=b32 -S settimeofday -k audit_time_rules If the system is 64-bit, then also add the following: # audit_time_rules -a always,exit -F arch=b64 -S settimeofday -k audit_time_rules
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208883r603263_rule'
OL6-00-000173: The audit system must be configured to audit all attempts to alter system time through /etc/localtime.
To determine if the system is configured to audit attempts to alter time via the /etc/localtime file, run the following command: $ sudo grep -w "/etc/localtime" /etc/audit/audit.rules If the system is configured to audit this activity, it will return a line. If the system is not configured to audit time changes, this is a finding.
Discussion
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
Fix
Add the following to "/etc/audit/audit.rules": -w /etc/localtime -p wa -k audit_time_rules The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport and should always be used.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208886r603263_rule'
OL6-00-000341: The snmpd service must not use a default password.
To ensure the default password is not set, run the following command: # grep -v "^#" /etc/snmp/snmpd.conf| grep public There should be no output. If there is output, this is a finding.
Discussion
Presence of the default SNMP password enables querying of different system aspects and could result in unauthorized knowledge of the system.
Fix
Edit "/etc/snmp/snmpd.conf", remove default community string "public". Upon doing that, restart the SNMP service: # service snmpd restart
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-209043r603263_rule'
OL6-00-000078: The system must implement virtual address space randomization.
The status of the "kernel.randomize_va_space" kernel parameter can be queried by running the following commands: $ sysctl kernel.randomize_va_space $ grep kernel.randomize_va_space /etc/sysctl.conf The output of the command should indicate a value of at least "1" (preferably "2"). If this value is not the default value, investigate how it could have been adjusted at runtime, and verify it is not set improperly in "/etc/sysctl.conf". If the correct value is not returned, this is a finding.
Discussion
Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code he or she has introduced into a process's address space during an attempt at exploitation. Additionally, ASLR also makes it more difficult for an attacker to know the location of existing code in order to repurpose it using return oriented programming (ROP) techniques.
Fix
To set the runtime status of the "kernel.randomize_va_space" kernel parameter, run the following command: # sysctl -w kernel.randomize_va_space=2 If this is not the system's default value, add the following line to "/etc/sysctl.conf": kernel.randomize_va_space = 2
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208848r603263_rule'
OL6-00-000189: The audit system must be configured to audit all discretionary access control permission modifications using fchownat.
To determine if the system is configured to audit calls to the "fchownat" system call, run the following command: $ sudo grep -w "fchownat" /etc/audit/audit.rules -a always,exit -F arch=b32 -S fchownat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchownat -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S fchownat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchownat -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "fchownat" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S fchownat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchownat -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S fchownat -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchownat -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208898r603263_rule'
OL6-00-000509: The system must forward audit records to the syslog service.
Verify the audispd plugin is active: # grep active /etc/audisp/plugins.d/syslog.conf If the "active" setting is missing or set to "no", this is a finding.
Discussion
The auditd service does not include the ability to send audit records to a centralized server for management directly. It does, however, include an audit event multiplexor plugin (audispd) to pass audit records to the local syslog server.
Fix
Set the "active" line in "/etc/audisp/plugins.d/syslog.conf" to "yes". Restart the auditd process. # service auditd restart
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-219587r603263_rule'
OL6-00-000031: The /etc/passwd file must not contain password hashes.
To check that no password hashes are stored in "/etc/passwd", run the following command: # awk -F: '($2 != "x") {print}' /etc/passwd If it produces any output, then a password hash is stored in "/etc/passwd". If any stored hashes are found in /etc/passwd, this is a finding.
Discussion
The hashes for all user account passwords should be stored in the file "/etc/shadow" and never in "/etc/passwd", which is readable by all users.
Fix
If any password hashes are stored in "/etc/passwd" (in the second field, instead of an "x"), the cause of this misconfiguration should be investigated. The account should have its password reset and the hash should be properly stored, or the account should be deleted entirely.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208808r603263_rule'
OL6-00-000154: The operating system must produce audit records containing sufficient information to establish what type of events occurred.
Run the following command to determine the current status of the "auditd" service: # service auditd status If the service is enabled, it should return the following: auditd is running... If the service is not running, this is a finding.
Discussion
Ensuring the "auditd" service is active ensures audit records generated by the kernel can be written to disk, or that appropriate actions will be taken if other obstacles exist.
Fix
The "auditd" service is an essential userspace component of the Linux Auditing System, as it is responsible for writing audit records to disk. The "auditd" service can be enabled with the following commands: # chkconfig auditd on # service auditd start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208877r603263_rule'
OL6-00-000342: The system default umask for the bash shell must be 077.
Verify the "umask" setting is configured correctly in the "/etc/bashrc" file by running the following command: # grep "umask" /etc/bashrc All output must show the value of "umask" set to 077, as shown below: # grep "umask" /etc/bashrc umask 077 umask 077 If the above command returns no output, or if the umask is configured incorrectly, this is a finding.
Discussion
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and/or written to by unauthorized users.
Fix
To ensure the default umask for users of the Bash shell is set properly, add or correct the "umask" setting in "/etc/bashrc" to read as follows: umask 077
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209044r603263_rule'
OL6-00-000106: The operating system must connect to external networks or information systems only through managed IPv6 interfaces consisting of boundary protection devices arranged in accordance with an organizational security architecture.
If the system is a cross-domain system, this is not applicable. If IPv6 is disabled, this is not applicable. Run the following command to determine the current status of the "ip6tables" service: # service ip6tables status If the service is not running, it should return the following: ip6tables: Firewall is not running. If the service is not running, this is a finding.
Discussion
The "ip6tables" service provides the system's host-based firewalling capability for IPv6 and ICMPv6.
Fix
The "ip6tables" service can be enabled with the following commands: # chkconfig ip6tables on # service ip6tables start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219549r603263_rule'
OL6-00-000019: There must be no .rhosts or hosts.equiv files on the system.
The existence of the file "/etc/hosts.equiv" or a file named ".rhosts" inside a user home directory indicates the presence of an Rsh trust relationship. If these files exist, this is a finding.
Discussion
Trust files are convenient, but when used in conjunction with the R-services, they can allow unauthenticated access to a system.
Fix
The files "/etc/hosts.equiv" and "~/.rhosts" (in each user's home directory) list remote hosts and users that are trusted by the local system when using the rshd daemon. To remove these files, run the following command to delete them from any location. # rm /etc/hosts.equiv $ rm ~/.rhosts
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-219547r603263_rule'
OL6-00-000521: The mail system must forward all mail for root to one or more system administrators.
Find the list of alias maps used by the Postfix mail server: # postconf alias_maps Query the Postfix alias maps for an alias for "root": # postmap -q root hash:/etc/aliases If there are no aliases configured for root that forward to a monitored email address, this is a finding.
Discussion
A number of system services utilize email messages sent to the root user to notify system administrators of active or impending issues. These messages must be forwarded to at least one monitored email address.
Fix
Set up an alias for root that forwards to a monitored email address: # echo "root: <system.administrator>@mail.mil" >> /etc/aliases # newaliases
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209065r603263_rule'
OL6-00-000051: Users must not be able to change passwords more than once every 24 hours.
To check the minimum password age, run the command: $ grep PASS_MIN_DAYS /etc/login.defs The DoD requirement is 1. If it is not set to the required value, this is a finding.
Discussion
Setting the minimum password age protects against users cycling back to a favorite password after satisfying the password reuse requirement.
Fix
To specify password minimum age for new accounts, edit the file "/etc/login.defs" and add or correct the following line, replacing [DAYS] appropriately: PASS_MIN_DAYS [DAYS] A value of 1 day is considered sufficient for many environments. The DoD requirement is 1.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208827r603263_rule'
OL6-00-000237: The system must not permit root logins using remote access programs such as ssh.
To determine how the SSH daemon's "PermitRootLogin" option is set, run the following command: # grep -i PermitRootLogin /etc/ssh/sshd_config If a line indicating "no" is returned, then the required value is set. If the required value is not set, this is a finding.
Discussion
Permitting direct root login reduces auditable information about who ran privileged commands on the system and also allows direct attack attempts on root's password.
Fix
The root user should never be allowed to log in to a system directly over a network. To disable root login via SSH, add or correct the following line in "/etc/ssh/sshd_config": PermitRootLogin no
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208925r603263_rule'
OL6-00-000247: The system clock must be synchronized continuously, or at least daily.
Run the following command to determine the current status of the "ntpd" service: # service ntpd status If the service is enabled, it should return the following: ntpd is running... If the service is not running, this is a finding.
Discussion
Enabling the "ntpd" service ensures that the "ntpd" service will be running and that the system will synchronize its time to any servers specified. This is important whether the system is configured to be a client (and synchronize only its own clock) or it is also acting as an NTP server to other systems. Synchronizing time is essential for authentication services such as Kerberos, but it is also important for maintaining accurate logs and auditing possible security breaches.
Fix
The "ntpd" service can be enabled with the following command: # chkconfig ntpd on # service ntpd start
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219562r603263_rule'
OL6-00-000281: The system package management tool must verify contents of all files associated with the audit package.
The following command will list which audit files on the system have file hashes different from what is expected by the RPM database. # rpm -V audit | awk '$1 ~ /..5/ && $2 != "c"' If there is output, this is a finding.
Discussion
The hash on important files like audit system executables should match the information given by the RPM database. Audit executables with erroneous hashes could be a sign of nefarious activity on the system.
Fix
The RPM package management system can check the hashes of audit system package files. Run the following command to list which audit files on the system have hashes that differ from what is expected by the RPM database: # rpm -V audit | grep '^..5' A "c" in the second column indicates that a file is a configuration file, which may appropriately be expected to change. If the file that has changed was not expected to then refresh from distribution media or online repositories. rpm -Uvh [affected_package] OR yum reinstall [affected_package]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209017r603263_rule'
OL6-00-000525: Auditing must be enabled at boot by setting a kernel parameter.
Inspect the kernel boot arguments (which follow the word "kernel") in "/etc/grub.conf". If they include "audit=1", then auditing is enabled at boot time. If auditing is not enabled at boot time, this is a finding.
Discussion
Each process on the system carries an "auditable" flag which indicates whether its activities can be audited. Although "auditd" takes care of enabling this for all processes which launch after it does, adding the kernel argument ensures it is set for every process during boot.
Fix
To ensure all processes can be audited, even those which start prior to the audit daemon, add the argument "audit=1" to the kernel line in "/boot/grub/grub.conf", in the manner below: kernel /vmlinuz-version ro vga=ext root=/dev/VolGroup00/LogVol00 rhgb quiet audit=1 UEFI systems may prepend "/boot" to the "/vmlinuz-version" argument.
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-209068r603263_rule'
OL6-00-000306: The operating system must detect unauthorized changes to software and information.
To determine that periodic AIDE execution has been scheduled, run the following command: # grep aide /etc/crontab /etc/cron.*/* If there is no output, this is a finding.
Discussion
By default, AIDE does not install itself for periodic execution. Periodically running AIDE may reveal unexpected changes in installed files.
Fix
AIDE should be executed on a periodic basis to check for changes. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check AIDE can be executed periodically through other means; this is merely one example.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-219575r603263_rule'
OL6-00-000188: The audit system must be configured to audit all discretionary access control permission modifications using fchown.
To determine if the system is configured to audit calls to the "fchown" system call, run the following command: $ sudo grep -w "fchown" /etc/audit/audit.rules -a always,exit -F arch=b32 -S fchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchown -F auid=0 -k perm_mod -a always,exit -F arch=b64 -S fchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchown -F auid=0 -k perm_mod If the system is 64-bit and does not return a rule for both "b32" and "b64" architectures, this is a finding. If the system is not configured to audit the "fchown" system call, this is a finding.
Discussion
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
Fix
At a minimum, the audit system should collect file permission changes for all users and root. Add the following to "/etc/audit/audit.rules": -a always,exit -F arch=b32 -S fchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b32 -S fchown -F auid=0 -k perm_mod If the system is 64-bit, then also add the following: -a always,exit -F arch=b64 -S fchown -F auid>=500 -F auid!=4294967295 \ -k perm_mod -a always,exit -F arch=b64 -S fchown -F auid=0 -k perm_mod
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208897r603263_rule'
OL6-00-000265: The ntpdate service must not be running.
To check that the "ntpdate" service is disabled in system boot configuration, run the following command: # chkconfig "ntpdate" --list Output should indicate the "ntpdate" service has either not been installed, or has been disabled at all runlevels, as shown in the example below: # chkconfig "ntpdate" --list "ntpdate" 0:off 1:off 2:off 3:off 4:off 5:off 6:off Run the following command to verify "ntpdate" is disabled through current runtime configuration: # service ntpdate status If the service is disabled the command will return the following output: ntpdate is stopped If the service is running, this is a finding.
Discussion
The "ntpdate" service may only be suitable for systems which are rebooted frequently enough that clock drift does not cause problems between reboots. In any event, the functionality of the ntpdate service is now available in the ntpd program and should be considered deprecated.
Fix
The ntpdate service sets the local hardware clock by polling NTP servers when the system boots. It synchronizes to the NTP servers listed in "/etc/ntp/step-tickers" or "/etc/ntp.conf" and then sets the local hardware clock to the newly synchronized system time. The "ntpdate" service can be disabled with the following commands: # chkconfig ntpdate off # service ntpdate stop
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208939r603263_rule'
OL6-00-000511: The audit system must take appropriate action when there are disk errors on the audit storage volume.
Inspect "/etc/audit/auditd.conf" and locate the following line to determine if the system is configured to take appropriate action when disk errors occur: # grep disk_error_action /etc/audit/auditd.conf disk_error_action = [ACTION] If the system is configured to "suspend" when disk errors occur or "ignore" them, this is a finding.
Discussion
Taking appropriate action in case of disk errors will minimize the possibility of losing audit records.
Fix
Edit the file "/etc/audit/auditd.conf". Modify the following line, substituting [ACTION] appropriately: disk_error_action = [ACTION] Possible values for [ACTION] are described in the "auditd.conf" man page. These include: "ignore" "syslog" "exec" "suspend" "single" "halt" Set this to "syslog", "exec", "single", or "halt".
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209059r603263_rule'
OL6-00-000214: The rshd service must not be running.
To check that the "rsh" service is disabled in system boot configuration, run the following command: # chkconfig "rsh" --list Output should indicate the "rsh" service has either not been installed, or has been disabled, as shown in the example below: # chkconfig "rsh" --list rsh off OR error reading information on service rsh: No such file or directory If the service is running, this is a finding.
Discussion
The rsh service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network.
Fix
The "rsh" service, which is available with the "rsh-server" package and runs as a service through xinetd, should be disabled. The "rsh" service can be disabled with the following command: # chkconfig rsh off
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-208915r603263_rule'
OL6-00-000033: The /etc/shadow file must be owned by root.
To check the ownership of "/etc/shadow", run the command: $ ls -l /etc/shadow If properly configured, the output should indicate the following owner: "root" If it does not, this is a finding.
Discussion
The "/etc/shadow" file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.
Fix
To properly set the owner of "/etc/shadow", run the command: # chown root /etc/shadow
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208810r603263_rule'
OL6-00-000053: User passwords must be changed at least every 60 days.
To check the maximum password age, run the command: $ grep PASS_MAX_DAYS /etc/login.defs The DoD requirement is 60. If it is not set to the required value, this is a finding.
Discussion
Setting the password maximum age ensures users are required to periodically change their passwords. This could possibly decrease the utility of a stolen password. Requiring shorter password lifetimes increases the risk of users writing down the password in a convenient location subject to physical compromise.
Fix
To specify password maximum age for new accounts, edit the file "/etc/login.defs" and add or correct the following line, replacing [DAYS] appropriately: PASS_MAX_DAYS [DAYS] The DoD requirement is 60.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208828r603263_rule'
OL6-00-000136: The operating system must back up audit records on an organization defined frequency onto a different system or media than the system being audited.
To ensure logs are sent to a remote host, examine the file "/etc/rsyslog.conf". If using UDP, a line similar to the following should be present: *.* @[loghost.example.com] If using TCP, a line similar to the following should be present: *.* @@[loghost.example.com] If using RELP, a line similar to the following should be present: *.* :omrelp:[loghost.example.com] If none of these are present, this is a finding.
Discussion
A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.
Fix
To configure rsyslog to send logs to a remote log server, open "/etc/rsyslog.conf" and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting "[loghost.example.com]" appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments. To use UDP for log message delivery: *.* @[loghost.example.com] To use TCP for log message delivery: *.* @@[loghost.example.com] To use RELP for log message delivery: *.* :omrelp:[loghost.example.com]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208873r603263_rule'
OL6-00-000027: The system must prevent the root account from logging in from virtual consoles.
To check for virtual console entries which permit root login, run the following command: # grep '^vc/[0-9]' /etc/securetty If any output is returned, then root logins over virtual console devices is permitted. If root login over virtual console devices is permitted, this is a finding.
Discussion
Preventing direct root login to virtual console devices helps ensure accountability for actions taken on the system using the root account.
Fix
To restrict root logins through the (deprecated) virtual console devices, ensure lines of this form do not appear in "/etc/securetty": vc/1 vc/2 vc/3 vc/4 Note: Virtual console entries are not limited to those listed above. Any lines starting with "vc/" followed by numerals should be removed.
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208804r603263_rule'
OL6-00-000211: The telnet daemon must not be running.
To check that the "telnet" service is disabled in system boot configuration, run the following command: # chkconfig "telnet" --list Output should indicate the "telnet" service has either not been installed, or has been disabled, as shown in the example below: # chkconfig "telnet" --list telnet off OR error reading information on service telnet: No such file or directory If the service is running, this is a finding.
Discussion
The telnet protocol uses unencrypted network communication, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. The telnet protocol is also subject to man-in-the-middle attacks. Mitigation: If an enabled telnet daemon is configured to only allow encrypted sessions, such as with Kerberos or the use of encrypted network tunnels, the risk of exposing sensitive information is mitigated.
Fix
The "telnet" service can be disabled with the following command: # chkconfig telnet off
Rating Info
DISA Cat I. NIST impact 4.
Expert Comment
Old Rule ID 'SV-219557r603263_rule'
OL6-00-000241: The SSH daemon must not permit user environment settings.
To ensure users are not able to present environment daemons, run the following command: # grep PermitUserEnvironment /etc/ssh/sshd_config If properly configured, output should be: PermitUserEnvironment no If it is not, this is a finding.
Discussion
SSH environment options potentially allow users to bypass access restriction in some configurations.
Fix
To ensure users are not able to present environment options to the SSH daemon, add or correct the following line in "/etc/ssh/sshd_config": PermitUserEnvironment no
Rating Info
DISA Cat III. NIST impact 2.
Expert Comment
Old Rule ID 'SV-208928r603263_rule'
OL6-00-000383: Audit log files must have mode 0640 or less permissive.
Run the following command to check the mode of the system audit logs: grep "^log_file" /etc/audit/auditd.conf|sed s/^[^\/]*//|xargs stat -c %a:%n Audit logs must be mode 0640 or less permissive. If any are more permissive, this is a finding.
Discussion
If users can write to audit logs, audit trails can be modified or destroyed.
Fix
Change the mode of the audit log files with the following command: # chmod 0640 [audit_file]
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-209053r603263_rule'
OL6-00-000125: The Stream Control Transmission Protocol (SCTP) must be disabled unless required.
If the system is configured to prevent the loading of the "sctp" kernel module, it will contain lines inside any file in "/etc/modprobe.d" or the deprecated"/etc/modprobe.conf". These lines instruct the module loading system to run another program (such as "/bin/true") upon a module "install" event. Run the following command to search for such lines in all files in "/etc/modprobe.d" and the deprecated "/etc/modprobe.conf": $ grep -r sctp /etc/modprobe.conf /etc/modprobe.d | grep -i “/bin/true” If no line is returned, this is a finding.
Discussion
Disabling SCTP protects the system against exploitation of any flaws in its implementation.
Fix
The Stream Control Transmission Protocol (SCTP) is a transport layer protocol, designed to support the idea of message-oriented communication, with several streams of messages within one connection. To configure the system to prevent the "sctp" kernel module from being loaded, add the following line to a file in the directory "/etc/modprobe.d": install sctp /bin/true
Rating Info
DISA Cat II. NIST impact 3.
Expert Comment
Old Rule ID 'SV-208867r603263_rule'