| name | cis-ubuntu1604-v200-3-5-3-3-4 |
| description | Ensure ip6tables firewall rules exist for all open ports |
| category | cis-networking |
| version | 2.0.0 |
| author | cyberstrike-official |
| tags | ["cis","ubuntu","linux","ubuntu-16.04","firewall"] |
| cis_id | 3.5.3.3.4 |
| 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 3.5.3.3.4
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.
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.
- 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. The last line identified by the "tcp dpt:22 state NEW" identifies it as a firewall rule for new connections on tcp port 22.
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 && output=
[ -n ] && -e || -e
