From Canonical Ubuntu 16.04 Security Technical Implementation Guide
Part of SRG-OS-000297-GPOS-00115
Associated with: CCI-000366 CCI-002080 CCI-002314
Failure to restrict network connectivity only to authorized systems permits inbound connections from malicious systems. It also permits outbound connections that may facilitate exfiltration of DoD data.
Verify the Uncomplicated Firewall is configured to employ a deny-all, allow-by-exception policy for allowing connections to other systems. Check the Uncomplicated Firewall configuration with the following command: # sudo ufw status Status: active To Action From -- ------ ---- [ 1] 22 LIMIT IN Anywhere If any services, ports, or applications are "allowed" and are not documented with the organization, this is a finding.
Configure the Uncomplicated Firewall to employ a deny-all, allow-by-exception policy for allowing connections to other systems. Remove any service that is not needed or documented by the organization with the following command (replace [NUMBER] with the rule number): # sudo ufw delete [NUMBER] Another option would be to set the Uncomplicated Firewall back to default with the following commands: # sudo ufw default deny incoming # sudo ufw default allow outgoing Note: UFW’s defaults are to deny all incoming connections and allow all outgoing connections.
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