“Firewall rules do not get applied properly to network traffic, and traffic that is not supposed to be allowed is allowed.”
Mullvad reported the PF firewall bug to Apple after the sixth Sonoma beta. It was still in the release candidate, two weeks before the September 26 launch. Every app that leans on PF inherits the leak, not just Mullvad’s. Mullvad found no workaround and is telling its users to stay on Ventura.