cyberstrikeus 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
- 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