Apple MacBooks Lose Network Connectivity After 49.7 Days Due to macOS “Time Bomb” Bug

Apple’s MacBook Neo, MacBook Air, and the latest MacBook Neo series of laptops are now susceptible to a significant performance drop if they remain powered on for 49.7 days without a reboot. Specifically, after exactly 49 days, 17 hours, 2 minutes, and 47.296 seconds of continuous operation, the entire TCP/IP networking stack shuts down and stops establishing new connections. This unusual bug stems from a kernel-level issue in Apple’s XNU kernel involving tcp_now, a 32-bit unsigned integer that tracks elapsed milliseconds since boot for the TCP stack. When it reaches its maximum value of 4,294,967,295, the counter stalls instead of resetting, disrupting the arithmetic macOS uses to expire and discard closed connections.

These inactive connection sessions accumulate quickly, increasing CPU usage as the system struggles to handle an ever-growing backlog. Once the available port pool, typically around 16,384 ports, is fully used, no new connections can be opened. Applications that rely on network access begin to fail, although already-established sessions continue to function, and the machine still responds to pings, albeit much more slowly. This initially delayed the diagnosis of the bug. A reboot resets the counter and restores normal operation, but the issue will recur on the same schedule after another 49.7 days of continuous use. There are potential solutions to fix the bug by using larger 64-bit integers, but this would require more extensive code changes, performance testing, and additional work compared to a simple fix.

The Photon team that discovered this issue notes that anyone managing a long-running MacBook should keep in mind the 49.7-day mandatory reboot until a fix is delivered. This is particularly important in enterprise environments, where managing machines is crucial for ensuring smooth operation without disrupting the workflow. The Photon team is also preparing a targeted workaround with the tcp_now that will address the connection freeze without requiring a restart, likely in the form of a live kernel patch or something similar. We need to wait and see how this will be implemented before the patch is delivered.