NixOS audit system must protect logon UIDs from unauthorized change.

If audit information were to become compromised, then forensic analysis and discovery of the true source of potentially malicious system activity is impossible to achieve.

Audit information includes all information (e.g., audit records, audit settings, audit reports) needed to successfully audit system activity.

In immutable mode, unauthorized users cannot execute changes to the audit system to potentially hide malicious activity and then put the audit rules back. A system reboot would be noticeable and a system administrator could then investigate the unauthorized changes.

Satisfies: SRG-OS-000058-GPOS-00028, SRG-OS-000059-GPOS-00029

Verify the audit system prevents unauthorized changes to logon UIDs with the following command:

$ sudo auditctl -s | grep -i immutable

loginuid_immutable 1 locked

If the command does not return "loginuid_immutable 1 locked", this is a finding.

Configure NixOS to prevent unauthorized changes to logon UIDs.

Add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix:

security.audit.rules = [ "--loginuid-immutable" ];

Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch