- A very strange bug in macOS has just been found
- If a Mac is on for (just over) 49 days, its network functionality will completely fail
- The only cure is apparently a reboot, but presumably Apple will now work on an official fix
Have you ever wondered what would happen if you left your Mac on for a few months? Probably not, but you might be interested to learn that if you did, the network side of the OS would fail.
Tom’s Hardware reports that Photon wrote a blog post about how it “found a ticking bomb in macOS TCP networks,” an explosive element of code that “detonates after exactly 49 days.”
Well, 49 days, 17 hours, two minutes and 47 seconds to be exact. Once macOS has run continuously for the exact amount of time, the operating system will experience an ‘integer overflow’ that “freezes the internal TCP timestamp clock”.
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When that happens, existing TCP network connections won’t expire as they should, remain frozen in place, and eventually, as Photon explains, “Ephemeral ports are slowly depleted, and eventually no new TCP connections can be established at all. ICMP (ping) keeps working. Everything else dies.”
In short, networking on Mac goes completely kaput and the only cure is to restart the machine. Yes, the old ‘turn it off and on again’ solution.
Photon — a company that facilitates the building of AI agents — found this bug on the Macs it uses to monitor Apple’s Messages service, and the company has successfully reproduced the bug on two systems.
Obviously, this isn’t an issue that most of you – assuming you own a Mac – will have to worry about. No regular user leaves their machine on for 50 days straight; but if you are ever inclined to do so, at least you are now warned. This is obviously more of a bug that will hit servers (running continuously for long periods of time) and one that companies like Photon need to be aware of.
As mentioned, the root cause of the problem is integer overflow. This is where macOS assumes that a counter will only increment in numerical value, when in fact it returns to zero after 50 days of incrementing – and this is also something that has caught Microsoft out in the past. Photon reminds us that Windows 95 suffered a similar crash for 49.7 days, when the kernel’s 32-bit millisecond tick counter overflowed, in this case causing the PC to completely freeze.
Photon is apparently working on a solution to avoid having to reboot to fix the Mac, but now that this bug has been brought to Apple’s attention, we should see an official fix before long.
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