NixOS must enable the built-in firewall.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-268078	SRG-OS-000298-GPOS-00116	ANIX-00-000010	SV-268078r1130947_rule	2025-08-19	1

Description
Without the ability to immediately disconnect or disable remote access, an attack or other compromise taking place would not be immediately stopped. Operating system remote access functionality must have the capability to immediately disconnect current users remotely accessing the information system and/or disable further remote access. The speed of disconnect or disablement varies based on the criticality of mission's functions and the need to eliminate immediate or future remote access to organizational information systems. The remote access functionality (e.g., RDP) may implement features such as automatic disconnect (or user-initiated disconnect) in case of adverse information based on an indicator of compromise or attack. Satisfies: SRG-OS-000298-GPOS-00116, SRG-OS-000096-GPOS-00050, SRG-OS-000297-GPOS-00115, SRG-OS-000480-GPOS-00232

Description

Without the ability to immediately disconnect or disable remote access, an attack or other compromise taking place would not be immediately stopped. Operating system remote access functionality must have the capability to immediately disconnect current users remotely accessing the information system and/or disable further remote access. The speed of disconnect or disablement varies based on the criticality of mission's functions and the need to eliminate immediate or future remote access to organizational information systems. The remote access functionality (e.g., RDP) may implement features such as automatic disconnect (or user-initiated disconnect) in case of adverse information based on an indicator of compromise or attack. Satisfies: SRG-OS-000298-GPOS-00116, SRG-OS-000096-GPOS-00050, SRG-OS-000297-GPOS-00115, SRG-OS-000480-GPOS-00232

ℹ️ Check
Verify NixOS has the network firewall enabled with the following command: $ sudo iptables -L \| grep nixos-fw-log-refuse nixos-fw-log-refuse all -- anywhere anywhere Verify the firewall panic tools are present: $ which firewall-panic /run/current-system/sw/bin/firewall-panic $ which firewall-panic-off /run/current-system/sw/bin/firewall-panic-off If the "nixos-fw-log-refuse all -- anywhere anywhere" firewall rule is not present and the firewall panic commands are not found, this is a finding.

ℹ️ Check

Verify NixOS has the network firewall enabled with the following command: $ sudo iptables -L | grep nixos-fw-log-refuse nixos-fw-log-refuse all -- anywhere anywhere Verify the firewall panic tools are present: $ which firewall-panic /run/current-system/sw/bin/firewall-panic $ which firewall-panic-off /run/current-system/sw/bin/firewall-panic-off If the "nixos-fw-log-refuse all -- anywhere anywhere" firewall rule is not present and the firewall panic commands are not found, this is a finding.

✔️ Fix
Update the NixOS config, typically stored either in /etc/nixos/configuration.nix or /etc/nixos/flake.nix, to enforce firewall rules by adding the following configuration settings: networking.firewall.enable = true; Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch