Title

Successful/unsuccessful uses of the chown, fchown, fchownat, and lchown system calls in RHEL 8 must generate an audit record. (Cat II impact)

Discussion

Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one. Audit records can be generated from various components within the information system (e.g., module or policy filter). The "chown" command is used to change file owner and group. The "fchown" system call is used to change the ownership of a file referred to by the open file descriptor. The "fchownat" system call is used to change ownership of a file relative to a directory file descriptor. The "lchown" system call is used to change the ownership of the file specified by a path, which does not dereference symbolic links. When a user logs on, the AUID is set to the UID of the account that is being authenticated. Daemons are not user sessions and have the loginuid set to "-1". The AUID representation is an unsigned 32-bit integer, which equals "4294967295". The audit system interprets "-1", "4294967295", and "unset" in the same way. The system call rules are loaded into a matching engine that intercepts each syscall made by all programs on the system. Therefore, it is very important to use syscall rules only when absolutely necessary since these affect performance. The more rules, the bigger the performance hit. The performance can be helped, however, by combining syscalls into one rule whenever possible. Satisfies: SRG-OS-000062-GPOS-00031, SRG-OS-000037-GPOS-00015, SRG-OS-000042-GPOS-00020, SRG-OS-000392-GPOS-00172, SRG-OS-000462-GPOS-00206, SRG-OS-000471-GPOS-00215, SRG-OS-000064-GPOS-00033, SRG-OS-000466-GPOS-00210

Check Content

Verify RHEL 8 generates an audit record upon successful/unsuccessful attempts to use the "chown", "fchown", "fchownat" and "lchown" system calls by using the following command to check the file system rules in "/etc/audit/audit.rules": $ sudo grep chown /etc/audit/audit.rules -a always,exit -F arch=b32 -S chown,fchown,fchownat,lchown -F auid>=1000 -F auid!=unset -k perm_mod -a always,exit -F arch=b64 -S chown,fchown,fchownat,lchown -F auid>=1000 -F auid!=unset -k perm_mod If audit rules are not defined for "chown", "fchown", "fchownat", and "lchown" or any of the lines returned are commented out, this is a finding.

Fix Text

Configure the audit system to generate an audit event for any successful/unsuccessful use of the "chown", "fchown", "fchownat", and "lchown" system calls by adding or updating the following line to "/etc/audit/rules.d/audit.rules": -a always,exit -F arch=b32 -S chown,fchown,fchownat,lchown -F auid>=1000 -F auid!=unset -k perm_mod -a always,exit -F arch=b64 -S chown,fchown,fchownat,lchown -F auid>=1000 -F auid!=unset -k perm_mod The audit daemon must be restarted for the changes to take effect.

Additional Identifiers

Rule ID: SV-230455r1017251_rule

Vulnerability ID: V-230455

Group Title: SRG-OS-000062-GPOS-00031

Expert Comments

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