Successful/unsuccessful uses of the chown, fchown, fchownat, and lchown system calls in NixOS must generate an audit record.

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).

Verify NixOS generates an audit record upon attempts to use the "chown", "fchown", "fchownat", and "lchown" system calls.

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

$ sudo auditctl -l | grep chown

-a always,exit -F arch=b32 -S lchown,fchown,chown,fchownat -F auid>=1000 -F auid!=-1 -F key=perm_mod -a always,exit -F arch=b64 -S chown,fchown,lchown,fchownat -F auid>=1000 -F auid!=-1 -F key=perm_mod

If the command does not return an audit rule for "chown", "fchown", "fchownat", and "lchown", 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.

Configure NixOS to generate audit records for any attempts to use the "chown", "fchown", "fchownat", and "lchown" 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 lchown,fchown,chown,fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod" "-a always,exit -F arch=b64 -S chown,fchown,lchown,fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod" ];

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