cyberstrikeus CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.5.3.2.4
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 -4tuln
Run the following command to determine firewall rules:
iptables -L INPUT -v -n
Verify all open ports listening on non-localhost addresses have at least one firewall rule.
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:
iptables -A INPUT -p <protocol> --dport <port> -m state --state NEW -j ACCEPT
References
None
CIS Controls
Version 7
9.2 Ensure Only Approved Ports, Protocols and Services Are Running - Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.
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.