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Tiny Deathstars of Foulness

The tools to automate OS X firewall events from the command line are still stored in /usr/libexec/ApplicationFirewall. And you will still use socketfilterfw there for much of the heavy lifting. However, now there are much more helpful and functional options in socketfilterfw that will allow you to more easily script the firewall.

Some tricks I’ve picked up with the Mac Firewall/alf scripting:

  • Configure the firewall fully before turning it on (especially if you’re doing so through something like Casper, FileWave, Munki, or Absolute Manage where you might kick yourself out of your session otherwise).
  • Whatever you do, you can always reset things back to defaults by removing the com.apple.alf.plist file from /Library/Preferences replacing it with the default plist from /usr/libexec/ApplicationFirewall/com.apple.alf.plist.
  • Configure global settings, then per-application settings, then enable the firewall. If a remote system, do ;wait; and then enable the first time to make sure everything works before enabling the firewall for good.
  • To debug, use the following command: “/usr/libexec/ApplicationFirewall/socketfilterfw -d”

In /usr/libexec/ApplicationFirewall is the Firewall command, the binary of the actual application layer firewall and socketfilterfw, which configures the firewall. To configure the firewall to block all incoming traffic:

/usr/libexec/ApplicationFirewall/socketfilterfw --setblockall on

To see if block all is enabled:

/usr/libexec/ApplicationFirewall/socketfilterfw --getblockall

The output would be as follows, if successful:

Firewall is set to block all non-essential incoming connections

A couple of global options that can be set. Stealth Mode:

/usr/libexec/ApplicationFirewall/socketfilterfw --setstealthmode on

To check if stealth mode is enabled:

/usr/libexec/ApplicationFirewall/socketfilterfw --getstealthmode

Firewall logging:

/usr/libexec/ApplicationFirewall/socketfilterfw --setloggingmode on

You can also control the verbosity of logs, using throttled, brief or detail. For example, if you need to troubleshoot some issues, you might set the logging to detail using the following command:

/usr/libexec/ApplicationFirewall/socketfilterfw --setloggingopt: detail

To start the firewall:

/usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on

While it would be nice to think that that was going to be everything for everyone, it just so happens that some environments actually need to allow traffic. Therefore, traffic can be allowed per signed binary. To allow signed applications:

/usr/libexec/ApplicationFirewall/socketfilterfw --setallowsigned on

To check if you allow signed apps:

/usr/libexec/ApplicationFirewall/socketfilterfw --getallowsigned

This will allow all TRUSTEDAPPS. The –listapps option shows the status of each filtered application:

/usr/libexec/ApplicationFirewall/socketfilterfw --listapps

To check if an app is blocked:

/usr/libexec/ApplicationFirewall/socketfilterfw –getappblocked /Applications/MyApp.app/Contents/MacOS/myapp

This shows the number of exceptions, explicitly allowed apps and signed exceptions as well as process names and allowed app statuses. There is also a list of TRUSTEDAPPS, which will initially be populated by Apple tools with sharing capabilities (e.g. httpd & smbd). If you are enabling the firewall using a script, first sign your applications that need to allow sharing but are not in the TRUSTEDAPPS section by using the -s option along with the application binary (not the .app bundle):

/usr/libexec/ApplicationFirewall/socketfilterfw -s /Applications/MyApp.app/Contents/MacOS/myapp

Once signed, verify the signature:

/usr/libexec/ApplicationFirewall/socketfilterfw -v /Applications/MyApp.app/Contents/MacOS/myapp

Once signed, trust the application using the –add option:

/usr/libexec/ApplicationFirewall/socketfilterfw --add /Applications/MyApp.app/Contents/MacOS/myapp

To see a list of trusted applications. You can do so by using the -l option as follows (the output is pretty ugly and needs to be parsed better):

/usr/libexec/ApplicationFirewall/socketfilterfw -l

If, in the course of your testing, you determine the firewall just isn’t for you, disable it:

/usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate off

To sanity check whether it’s started:

/usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate

Or to manually stop it using launchctl (should start again with a reboot):

launchctl unload /System/Library/LaunchAgents/com.apple.alf.useragent.plist
launchctl unload /System/Library/LaunchDaemons/com.apple.alf.agent.plist

If you disable the firewalll using launchctl, you may need to restart services for them to work again.

July 16th, 2015

Posted In: Mac OS X, Mac OS X Server, Mac Security, Mass Deployment

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