Title

An application firewall must employ a deny-all, allow-by-exception policy for allowing connections to other systems. (Cat II impact)

Discussion

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. Satisfies: SRG-OS-000297-GPOS-00115, SRG-OS-000480-GPOS-00231

Check Content

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.

Fix Text

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.

Additional Identifiers

Rule ID: SV-90487r2_rule

Vulnerability ID: V-75807

Group Title:

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.