Vulnerability 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 "fchmodat" system call is used to change permissions of a file relative to a directory file descriptor.

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.

Satisfies: SRG-OS-000062-GPOS-00031, SRG-OS-000037-GPOS-00015, SRG-OS-000042-GPOS-00020, SRG-OS-000062-GPOS-00031, 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

Verify RHEL 8 generates an audit record when successful/unsuccessful attempts to use the "fchmodat" system call by performing the following command to check the file system rules in "/etc/audit/audit.rules":

$ sudo grep -w fchmodat /etc/audit/audit.rules

-a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -k perm_mod
-a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -k perm_mod

If the command does not return a line, or the line is commented out, this is a finding.

Fix

Configure the audit system to generate an audit event for any successful/unsuccessful use of the "fchmodat" system call by adding or updating the following lines to "/etc/audit/rules.d/audit.rules":

-a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -k perm_mod
-a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -k perm_mod

The audit daemon must be restarted for the changes to take effect.