Mullvad VPN announced that macOS users may experience traffic leaks after applying recent system updates due to a firewall malfunction.
According to
a bulletin published earlier today on Mullvad’s blog, the macOS firewall fails to enforce certain routing rules properly, allowing some applications to bypass the VPN tunnel and send traffic outside of it.
Mullvad has found that Apple’s own apps and services are excluded from the firewall, and hence sensitive user traffic is sent directly to its destination without getting encrypted. This includes iCloud, Siri, location services, the App Store, Apple Mail, and Messages, so the potential for privacy breaches and exposure to internet service providers (ISPs) or other intermediary observers is now present.
Most worryingly, the issue has been observed from macOS version 14.6 up until the most recent beta of 15.1, so it impacts a large number of Apple users.
A
similar issue was discovered by Mullvad VPN prior to the release of macOS 14 Sonoma, in September 2023, but Apple fixed it before the OS was rolled out to eligible devices. Apparently, the traffic leak due to firewall misconfigurations has now been re-introduced by to a faulty system update.
The Sequoia release has had its fair share of VPN problems since its release. Users
reported on Reddit last month that they encountered problems setting up a secure connection with some products. Experts claimed the issue stemmed from how the built-in firewall handled UDP traffic, causing DNS failures and also impacting security tools.
This time, the cause of the problem is unknown, and Mullvad VPN says it has already contacted Apple to ask for a resolution. Meanwhile their investigation to discover exactly what causes the leaks is still underway.
Impact and testing
Mullvad told RestorePrivacy that while they have not tested other VPN software on macOS to determine their operational status, it’s safe to assume that it affects any software that uses the packet filter (PF) firewall in macOS.
The VPN vendor also provided instructions for users in critical need of internet traffic security and privacy on how to check whether or not they’re leaking traffic.
To run the test, enter the following commands on a terminal:
Note that that running the test will temporarily block all traffic, so you will lose internet connectivity on your device until the changes are reversed. Also, the commands provided by Mullvad temporarily modify the packet filter rules, so if you have custom firewall rules, you should back them up before running the tests to avoid losing them.
