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

DevOps & Security
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Ensure nftables rules are permanent

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_18.04_LTS_Benchmark_v2.2.0/cis-ubuntu1804-v220-3-4-2-10/SKILL.md

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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

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