Vulnerability Discussion

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing discretionary access control (DAC) modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Satisfies: SRG-OS-000037-GPOS-00015, SRG-OS-000062-GPOS-00031, SRG-OS-000392-GPOS-00172, SRG-OS-000462-GPOS-00206, SRG-OS-000471-GPOS-00215

Check

Verify that OL 9 generates an audit record for all uses of the umount2 system call with the following commands:

$ sudo grep "umount2" /etc/audit/audit.rules

$ sudo sh -c 'grep "umount2" /etc/audit/audit.rules'

If the system is configured to audit this activity, it will return a line.

If no line is returned, this is a finding.

Fix

Configure the audit system to generate an audit event for any successful/unsuccessful use of the umount2 system call by adding the following rules to a rules file in /etc/audit/rules.d/ directory: (Example /etc/audit/rules.d/audit.rules)

-a always,exit -F arch=b32 -S umount2 -F auid>=1000 -F auid!=unset -k perm_mod
-a always,exit -F arch=b64 -S umount2 -F auid>=1000 -F auid!=unset -k perm_mod

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

Restart auditd:
$ sudo service auditd restart