Cis Ubuntu2004 V300 4 4 3 3

CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0 - Control 4.4.3.3

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:

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/env bash

{
  l_ipv6_enabled="is"
  ! grep -Pqs -- '^\h*0\b' /sys/module/ipv6/parameters/disable && l_ipv6_enabled="is not"
  if sysctl net.ipv6.conf.all.disable_ipv6 | grep -Pqs -- "^\h*net\.ipv6\.conf\.all\.disable_ipv6\h*=\h*1\b" \
  && \
    sysctl net.ipv6.conf.default.disable_ipv6 | grep -Pqs -- "^\h*net\.ipv6\.conf\.default\.disable_ipv6\h*=\h*1\b"; then
      l_ipv6_enabled="is not"
  fi
  echo -e " - IPv6 $l_ipv6_enabled enabled on the system"
}

Expected Result

Output should show rules matching site policy for outbound and established IPv6 connections. Or IPv6 is disabled.

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 INPUT -p tcp -m state --state ESTABLISHED -j ACCEPT
ip6tables -A INPUT -p udp -m state --state ESTABLISHED -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