Title

The audit system must be configured to audit all discretionary access control permission modifications using fchmodat. (Cat III impact)

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.

Check Content

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.

Fix Text

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

Additional Identifiers

Rule ID: SV-217965r603264_rule

Vulnerability ID: V-217965

Group Title: SRG-OS-000064

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.