cis-ubuntu1604-v200-3-5-3-2-3

name	cis-ubuntu1604-v200-3-5-3-2-3
description	Ensure iptables 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	3.5.3.2.3
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 3.5.3.2.3

Profile

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

Description

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

Notes:

• 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:

iptables -L -v -n

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:

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

References

None

CIS Controls

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.