The OS X system firewall must be configured with a default-deny policy.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-75997	AOSX-12-000155	SV-90685r1_rule		Medium

Description
An approved firewall must be installed and enabled to work in concert with the OS X Application Firewall. When configured correctly, firewalls protect computers from network attacks by blocking or limiting access to open network ports.

STIG	Date
Apple OS X 10.12 Security Technical Implementation Guide	2018-12-24

Details

Check Text ( C-75681r1_chk )
Ask the System Administrator (SA) or Information System Security Officer (ISSO) if an approved firewall is loaded on the system. The recommended system is the McAfee HBSS. If no firewall is installed on the system, this is a finding. If a firewall is installed and it is not configured with a "default-deny" policy, this is a finding.

Fix Text (F-82635r1_fix)
Install an approved HBSS or firewall solution onto the system and configure it with a "default-deny" policy.