Software developer Photon recently posted about a curious bug that they found in macOS involving TCP networking, which is widely used by computers for internet connectivity. Apparently, if a Mac that’s online is left on for exactly 49 days, 17 hours, 2 minutes, and 47 seconds, the Internet connection stops working.
The issue does have a fix: restart the Mac. This resets the connections and gets them working again. However, the countdown also restarts, so if the Mac is left on for another 49 days, 17 hours, 2 minutes, and 47 seconds, the bug makes its appearance again, and the Mac needs to be restarted.
Photon’s post provides details on the root of the problem, which involves a 32-bit integer overflow in the macOS XNU kernel. Photon says there’s a flaw in the way Transmission Control Protocol (TCP) timestamps are tracked, causing connections to stop working after 49 days.
Most people, however, have never experienced this bug because they’ve restarted their Mac for some reason, usually to complete an installation of a macOS update. Apple just released macOS 26.4.1, which came two weeks after macOS 26.4, so those are two instances where a Mac had to restart recently.
Photon is working on a fix for the bug, though its post does not say whether Apple has been notified. We expect Apple will issue a fix in a future macOS update. It’s also not clear what versions of macOS are affected.
If you are running a Mac that needs to stay on all the time, such as a server, you should restart it at a convenient time, just in case. You can see how long a Mac has been left on by using the Terminal by typing uptime and then pressing Return. Utilities such as Particulars and iStatMenus allow provide uptime statistics.
