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 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

To determine if the system is configured to audit calls to the umount2 system call, run the following command:

$ sudo auditctl -l | grep umount2

-a always,exit -F arch=b64 -S umount2 -F auid>=1000 -F auid!=-1 -F key=privileged-umount
-a always,exit -F arch=b32 -S umount2 -F auid>=1000 -F auid!=-1 -F key=privileged-umount

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 or updating the following rules in a file in "/etc/audit/rules.d".

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

To load the rules to the kernel immediately, use the following command:

$ sudo augenrules --load