cis-ubuntu2004-v300-4-4-3-4

name	cis-ubuntu2004-v300-4-4-3-4
description	Ensure ip6tables firewall rules exist for all open ports
category	cis-networking
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","firewall","iptables"]
cis_id	4.4.3.4
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0 - Control 4.4.3.4

Profile

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

Description

Any ports that have been opened on non-loopback addresses need firewall rules to govern traffic.

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
• The remediation command opens up the port to traffic from all sources. Consult iptables documentation and set any restrictions in compliance with site policy

Rationale

Without a firewall rule configured for open ports default firewall policy will drop all packets to these ports.

Audit Procedure

Command Line

Run the following command to determine open ports:

ss -6tuln

Run the following command to determine firewall rules:

ip6tables -L INPUT -v -n

Verify all open ports listening on non-localhost addresses have at least one firewall rule.

Expected Result

All open IPv6 ports on non-localhost addresses have corresponding ip6tables rules.

Remediation

Command Line

For each port identified in the audit which does not have a firewall rule establish a proper rule for accepting inbound connections:

ip6tables -A INPUT -p <protocol> --dport <port> -m state --state NEW -j ACCEPT

Default Value

Not applicable.

References

1. NIST SP 800-53 Rev. 5: CA-9, SC-7

CIS Controls

v8 - 4.4 Implement and Manage a Firewall on Servers v8 - 4.5 Implement and Manage a Firewall on End-User Devices v7 - 9.4 Apply Host-based Firewalls or Port Filtering

MITRE ATT&CK Mappings: T1562, T1562.004 | TA0011 | M1031, M1037