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

DevOps & Security
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Ensure ip6tables outbound and established connections are configured

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_16.04_LTS_Benchmark_v2.0.0/cis-ubuntu1604-v200-3-5-3-3-3/SKILL.md

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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:

ip6tables -L -v -n

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

#!/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:

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.