2.5.2.1 Ensure Firewall Is Enabled

Information

A firewall is a piece of software that blocks unwanted incoming connections to a system. Apple has posted general documentation about the application firewall:

http://support.apple.com/en-us/HT201642

Rationale:

A firewall minimizes the threat of unauthorized users gaining access to your system while connected to a network or the Internet.

Impact:

The firewall may block legitimate traffic. Applications that are unsigned will require special handling.

Solution

Perform the following to turn the firewall on:
Graphical Method:

Open System Preferences

Select Security & Privacy

Select Firewall

Select Turn On Firewall

Terminal Method:
Run the following command to enable the firewall:

$ sudo /usr/bin/defaults write /Library/Preferences/com.apple.alf globalstate -int <value>

For the <value>, use either 1, specific services, or 2, essential services only.
Profile Method:

Create or edit a configuration profile with the PayLoadType of com.apple.firewall

Add the key EnableFirewall

Set the key to <true/>

See Also

https://workbench.cisecurity.org/files/4000