cis-ubuntu1804-v220-3-4-3-3-3

name	cis-ubuntu1804-v220-3-4-3-3-3
description	Ensure ip6tables outbound and established connections are configured
category	cis-networking
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","networking","firewall","iptables","ipv6"]
cis_id	3.4.3.3.3
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 3.4.3.3.3

Description

Configure the firewall rules for new outbound, and established IPv6 connections.

Rationale

If rules are not in place for new outbound, and established connections all packets will be dropped by the default policy preventing network usage.

Impact

• Changing firewall settings while connected over network can result in being locked out of the system
• Remediation will only affect the active system firewall, be sure to configure the default policy in your firewall management to apply on boot as well

Audit Procedure

Command Line

Run the following command and verify all rules for new outbound, and established connections match site policy:

ip6tables -L -v -n

-OR-

Verify IPv6 is disabled: Run the following script. Output will confirm if IPv6 is enabled on the system.

#!/usr/bin/bash
{
  if grep -Pqs '^\h*0\b' /sys/module/ipv6/parameters/disable; then
    echo -e " - IPv6 is enabled on the system"
  else
    echo -e " - IPv6 is not enabled on the system"
  fi
}

Expected Result

The output should show rules matching site policy for outbound and established IPv6 connections. Or IPv6 is not enabled on the system.

Remediation

Command Line

Configure iptables in accordance with site policy. The following commands will implement a policy to allow all outbound connections and all established connections:

ip6tables -A OUTPUT -p tcp -m state --state NEW,ESTABLISHED -j ACCEPT
ip6tables -A OUTPUT -p udp -m state --state NEW,ESTABLISHED -j ACCEPT
ip6tables -A OUTPUT -p icmp -m state --state NEW,ESTABLISHED -j ACCEPT
ip6tables -A INPUT -p tcp -m state --state ESTABLISHED -j ACCEPT
ip6tables -A INPUT -p udp -m state --state ESTABLISHED -j ACCEPT
ip6tables -A INPUT -p icmp -m state --state ESTABLISHED -j ACCEPT

Default Value

No connection tracking rules exist 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