How to stop the macOS firewall leaking system network data after a software update
How to stop the macOS firewall leaking system network data after a software update
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macOS Sequoia can sometimes leak data after an update. Several sources report the firewall in macOS Sequoia can sometimes leak data after an update. Here's how to test and fix it. The macOS firewall in System Settings allows you to protect your Mac and filter network traffic based on a set of rules.
Several sites, including mullvad.net have reported that after macOS Sequoia updates, the firewall built into macOS may leak some data, allowing it to avoid firewall rules. The cause of this leak is unknown - but apparently, a Mac restart fixes the problem after updating.
Being based on BSD, macOS uses a packet-based network filter known simply as Packet Filter or "PF" for short (also known as Berkeley Packet Filter). PF goes way back to the early versions of BSD and OpenBSD when networking was added to UNIX. PF works based on a set of rules stored in a file, which on macOS is named pf.conf that lives at the root of your Startup Disk in /private/etc. You'll need to turn on invisible files in the macOS Finder, or use the command line in Terminal to view the file.
You can open pf.conf in TextEdit but if you change the contents of the file be sure you understand PF and how the rules file works. You can learn more about pf.conf in Terminal by typing:. man pf.conf and pressing Return. pf.conf also points to a folder in /private/etc named pf.anchors which contains sets of individual rules based on domains.