An application firewall must be enabled on the system.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-215112	UBTU-16-030040	SV-215112r610931_rule		Medium

Description
Firewalls protect computers from network attacks by blocking or limiting access to open network ports. Application firewalls limit which applications are allowed to communicate over the network.

STIG	Date
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide	2020-12-09

Details

Check Text ( C-16311r285204_chk )
Verify the Uncomplicated Firewall is enabled on the system by running the following command: # sudo systemctl is-enabled ufw enabled If the above command returns the status as "disabled", this is a finding. If the Uncomplicated Firewall is not installed, ask the System Administrator if another application firewall is installed. If no application firewall is installed this is a finding.

Fix Text (F-16309r285205_fix)
Enable the Uncomplicated Firewall by using the following commands: # sudo systemctl start ufw # sudo systemctl enable ufw