OL 8 must generate audit records for any use of the "unlink" command.

STIG ID: OL08-00-030364  |  SRG: SRG-OS-000037-GPOS-00015 | Severity: medium |  CCI: CCI-000130,CCI-000135,CCI-000169,CCI-000172,CCI-002884

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 "unlink" command deletes a name from the filesystem. If that name was the last link to a file and no processes have the file open, the file is deleted and the space it was using is made available for reuse.

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-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

Check

Verify OL 8 is configured to audit successful file unlinking by running the following command:

$ sudo grep -w "unlink" /etc/audit/audit.rules

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

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

Note: The "-k" allows for specifying an arbitrary identifier, and the string after it does not need to match the example output above.

Fix

Configure OL 8 to audit successful file unlinking by adding or updating the following lines to "/etc/audit/rules.d/audit.rules":

-a always,exit -F arch=b32 -S unlink -F success=1 -F auid>=1000 -F auid!=unset -k delete

-a always,exit -F arch=b64 -S unlink -F success=1 -F auid>=1000 -F auid!=unset -k delete

The audit daemon must be restarted for the changes to take effect. To restart the audit daemon, run the following command:

$ sudo service auditd restart
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