CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.4.2.10

---
name: cis-ubuntu1804-v220-3-4-2-10-858ba0ece485
description: "Ensure nftables rules are permanent"
category: cis-networking
version: "2.2.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-18.04, networking, firewall, nftables]
cis_id: "3.4.2.10"
cis_benchmark: "CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.4.2.10

## Description

nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames.

The nftables service reads the `/etc/nftables.conf` file for a nftables file or files to include in the nftables ruleset.

A nftables ruleset containing the input, forward, and output base chains allow network traffic to be filtered.

## Rationale

Changes made to nftables ruleset only affect the live system, you will also need to configure the nftables ruleset to apply on boot.

## Impact

None.

## Audit Procedure

### Command Line

Run the following commands to verify that input, forward, and output base chains are configured to be applied to a nftables ruleset on boot:

Run the following command to verify the input base chain:

```bash
[ -n "$(grep -E '^\s*include' /etc/nftables.conf)" ] && awk '/hook input/,/}/' $(awk '$1 ~ /^\s*include/ { gsub("\"","",$2);print $2 }' /etc/nftables.conf)
```

Run the following command to verify the forward base chain:

```bash
[ -n "$(grep -E '^\s*include' /etc/nftables.conf)" ] && awk '/hook forward/,/}/' $(awk '$1 ~ /^\s*include/ { gsub("\"","",$2);print $2 }' /etc/nftables.conf)
```

Run the following command to verify the output base chain:

```bash
[ -n "$(grep -E '^\s*include' /etc/nftables.conf)" ] && awk '/hook output/,/}/' $(awk '$1 ~ /^\s*include/ { gsub("\"","",$2);print $2 }' /etc/nftables.conf)
```

Review each base chain to ensure that it follows local site policy.

## Expected Result

Each command should return the corresponding base chain configuration with rules matching site policy.

## Remediation

### Command Line

Edit the `/etc/nftables.conf` file and un-comment or add a line with `include <Absolute path to nftables rules file>` for each nftables file you want included in the nftables ruleset on boot.

Example:

```bash
vi /etc/nftables.conf
```

Add the line:

```
include "/etc/nftables.rules"
```

## Default Value

No nftables rules are permanent by default.

## References

1. NIST SP 800-53 Rev. 5: CA-9, SC-7
2. CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0

## CIS Controls

Version 8

4.4 Implement and Manage a Firewall on Servers - Implement and manage a firewall on servers, where supported.

4.5 Implement and Manage a Firewall on End-User Devices - Implement and manage a host-based firewall or port-filtering tool on end-user devices.

Version 7

9.4 Apply Host-based Firewalls or Port Filtering - Apply host-based firewalls or port filtering tools on end systems, with a default-deny rule that drops all traffic except those services and ports that are explicitly allowed.

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## Assessment Status

Automated