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

NixOS must terminate all SSH connections after becoming unresponsive.

DISA Rule

SV-268143r1131089_rule

Vulnerability Number

V-268143

Group Title

SRG-OS-000163-GPOS-00072

Rule Version

ANIX-00-001000

Severity

CAT II

CCI(s)

• CCI-001133 - Terminate the network connection associated with a communications session at the end of the session or after an organization-defined time period of inactivity.

Weight

10

Fix Recommendation

Configure NixOS to automatically terminate all network connections associated with SSH traffic after being unresponsive.

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

services.openssh.extraConfig = ''
ClientAliveCountMax 1
'';

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

Check Contents

Verify that all network connections associated with SSH traffic are automatically terminated after becoming unresponsive with the following command:

$ grep -i clientalivecount /etc/ssh/sshd_config

ClientAliveCountMax 1

If "ClientAliveCountMax" is not set to "1", is commented out, or is missing, this is a finding.

Vulnerability Number

V-268143

Documentable

False

Rule Version

ANIX-00-001000

Severity Override Guidance

Verify that all network connections associated with SSH traffic are automatically terminated after becoming unresponsive with the following command:

$ grep -i clientalivecount /etc/ssh/sshd_config

ClientAliveCountMax 1

If "ClientAliveCountMax" is not set to "1", is commented out, or is missing, this is a finding.

Check Content Reference

M

Target Key

5658