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        Why the macOS "49-Day" Networking Bug Probably Won't Affect You

   Adam Engst

   Photon, a company that develops a framework for connecting software
   agents to multiple messaging platforms, found a bug in macOS that
   causes TCP networking to fail sometime after 49 days of uptime. [1]It
   sounds dire:

     Every Mac has a hidden expiration date. After exactly 49 days, 17
     hours, 2 minutes, and 47 seconds of continuous uptime, a 32-bit
     unsigned integer overflow in Apple's XNU kernel freezes the internal
     TCP timestamp clock. Once frozen, TIME_WAIT connections never
     expire, ephemeral ports slowly exhaust, and eventually no new TCP
     connections can be established at all. ICMP (ping) keeps working.
     Everything else dies. The only fix most people know is a reboot. We
     discovered this bug on our iMessage service monitoring fleet,
     reproduced it live on two machines, and traced the root cause to a
     single comparison in the XNU kernel source.

   I don't recommend reading Photon's exhaustively detailed post (which
   reads like it may have been generated by an AI) unless you're extremely
   familiar with TCP networking code. Nevertheless, with some additional
   background from a [2]Hacker News discussion, it seems that most people
   don't need to worry about it because:
     * Most consumer Macs are rebooted for security updates well before
       reaching 49 days of uptime. Or at least they should be! Keep
       installing those updates.
     * Although Apple doesn't guarantee updates within 49 days, the bug
       doesn't cause instant failure at the 49-day mark. It merely
       prevents new TCP connections from being established. On a lightly
       used Mac, the resulting port exhaustion could take considerably
       longer to become noticeable.
     * If the Mac sleeps, the time could be significantly longer than 49
       days.
     * It appears that the bug originated in the XNU kernel in macOS 26,
       so previous versions shouldn't be affected. I suspect that many
       people with Mac media servers and other seldom-restarted Macs often
       aren't running the latest version of macOS.
     * Assuming that Photon has reported this bug to Apple (I couldn't
       find any discussion of it in the [3]Apple Developer Forums), it
       should be straightforward to fix in the upcoming macOS 26.5.

   That said, the bug does appear to be real, so if you have a macOS
   26-based server that doesn't sleep, it might be worth watching it'or
   restarting proactively if it's remote'when its uptime reaches 49 days.

   To see how long your Mac has been running since the last restart, open
   Terminal and enter the command uptime. I'm at 15 days on my main Mac.
   Anyone out there running macOS 26 with an uptime over 49 days?

   

References

   Visible links
   1. https://photon.codes/blog/we-found-a-ticking-time-bomb-in-macos-tcp-networking
   2. https://news.ycombinator.com/item?id=47667222
   3. https://developer.apple.com/forums/

   Hidden links:
   4. https://tidbits.com/uploads/2026/04/uptime.png

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