Cis Ubuntu1604 V200 3 5 3 3 3

---
name: cis-ubuntu1604-v200-3-5-3-3-3
description: "Ensure ip6tables outbound and established connections are configured"
category: cis-networking
version: "2.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-16.04, firewall]
cis_id: "3.5.3.3.3"
cis_benchmark: "CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.5.3.3.3

## Profile

- **Level:** Level 1 - Server, Level 1 - Workstation
- **Assessment Status:** Manual

## Description

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

Note:

- 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.

## 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.

## Audit Procedure

### Command Line

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

```bash
ip6tables -L -v -n
```

OR verify IPv6 is disabled. Run the following script. Output will confirm if IPv6 is disabled on the system.

```bash
#!/usr/bin/bin/bash

output=""
grubfile="$(find -L /boot -name 'grub.cfg' -type f)"
[ -f "$grubfile" ] && ! grep "^\s*linux" "$grubfile" | grep -vq ipv6.disable=1 && output="ipv6 disabled in grub config"
grep -Eqs "^\s*net\.ipv6\.conf\.all\.disable_ipv6\s*=\s*1\b" /etc/sysctl.conf /etc/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /run/sysctl.d/*.conf && grep -Eqs "^\s*net\.ipv6\.conf\.default\.disable_ipv6\s*=\s*1\b" /etc/sysctl.conf /etc/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /run/sysctl.d/*.conf && sysctl net.ipv6.conf.all.disable_ipv6 | grep -Eq "^\s*net\.ipv6\.conf\.all\.disable_ipv6\s*=\s*1\b" && sysctl net.ipv6.conf.default.disable_ipv6 | grep -Eq "^\s*net\.ipv6\.conf\.default\.disable_ipv6\s*=\s*1\b" && output="ipv6 disabled in sysctl config"
[ -n "$output" ] && echo -e "\n$output" || echo -e "\n*** IPv6 is 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:

```bash
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
```

## References

None

## CIS Controls

Version 6

9.1 Limit Open Ports, Protocols, and Services - Ensure that only ports, protocols, and services with validated business needs are running on each system.

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.