STIGQter: STIG Summary: Anduril NixOS Security Technical Implementation Guide Version: 1 Release: 2 Benchmark Date: 01 Oct 2025:

Successful/unsuccessful uses of the chmod, fchmod, and fchmodat system calls in NixOS must generate an audit record.

DISA Rule

SV-268100r1131002_rule

Vulnerability Number

V-268100

Group Title

SRG-OS-000042-GPOS-00020

Rule Version

ANIX-00-000380

Severity

CAT II

CCI(s)

• CCI-000135 - Generate audit records containing the organization-defined additional information that is to be included in the audit records.
• CCI-000172 - Generate audit records for the event types defined in AU-2 c that include the audit record content defined in AU-3.

Weight

10

Fix Recommendation

Configure NixOS to generate audit records for any attempts to use the "chmod", "fchmod", and "fchmodat" system calls.

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

security.audit.rules = [
"-a always,exit -F arch=b32 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=unset -k perm_mod"
"-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=unset -k perm_mod"
];

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

Check Contents

Verify NixOS generates an audit record upon attempts to use the "chmod", "fchmod", and "fchmodat" system calls.

Check the auditing rules currently loaded into the audit daemon with the following command:

$ sudo auditctl -l | grep chmod

-a always,exit -F arch=b32 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=-1 -k perm_mod
-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=-1 -k perm_mod

If the command does not return an audit rule for "chmod", "fchmod", and "fchmodat, this is a finding.

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

Vulnerability Number

V-268100

Documentable

False

Rule Version

ANIX-00-000380

Severity Override Guidance

Verify NixOS generates an audit record upon attempts to use the "chmod", "fchmod", and "fchmodat" system calls.

Check the auditing rules currently loaded into the audit daemon with the following command:

$ sudo auditctl -l | grep chmod

-a always,exit -F arch=b32 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=-1 -k perm_mod
-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=-1 -k perm_mod

If the command does not return an audit rule for "chmod", "fchmod", and "fchmodat, this is a finding.

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

Check Content Reference

M

Target Key

5658