cis-ubuntu1804-v220-3-4-2-10

name	cis-ubuntu1804-v220-3-4-2-10
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:

[ -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:

[ -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:

[ -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:

vi /etc/nftables.conf