Kernel Bug: Integer Overflow in Apple's XNU Stops TCP Packets – with Long Uptime
49 days, 17 hours, 2 minutes and 47 seconds: According to researchers, an integer overflow occurs on the Mac after this usage time. TCP connections fail.
Ethernet Connector: After 50 days, you should better restart your Mac once.
(Image: alexskopje / Shutterstock.com)
Anyone running their Mac for a long time, for example as a server, can encounter problems with network connections. According to security researchers from the agentic AI company Photon, macOS systems should not be operated beyond an uptime of almost 50 days. After exactly 49 days, 17 hours, 2 minutes, and 47 seconds, a problem in Apple's XNU kernel becomes visible. The internal TCP timestamp clock fails with an unsigned 32-bit integer overflow. If it freezes, TCP TIME_WAIT connections are no longer terminated, and actually temporary ports are no longer released. After some time, this leads to new TCP connections no longer being possible and network access failing. Insidious: Ping packets via ICMP still go through, so it's not initially possible to determine the problem.
The Uptime Phenomenon
According to Photon, the problem has existed since macOS Catalina (10.15, released in 2019). However, there have not been many error reports from users. The reason is likely that Macs usually have a long uptime, but Apple regularly publishes updates that then require a restart. Developer Michael Tsai writes that he has not yet experienced the problem despite months of using a Mac server. However, he has not yet installed Tahoe (macOS 26).
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Continuously active Macs are often used as file servers, among other things. Recently, Mac minis have become increasingly popular as OpenClaw machines, and Perplexity had also announced its agentic system „Personal Computer“ for the small desktop computer. Mac notebooks can also have a high uptime. They are usually only activated by opening the display. macOS users are not familiar with completely shutting down and later starting up again when using them again, as was often the standard with PC notebooks back then – instead, the machines, just like desktops, have been put to sleep for decades when not in use.
Only Reboot Helps
Photon did not provide information on whether the error was reported to Apple. However, the company has likely seen the analysis and will fix the problem shortly, if possible. Currently, if it occurs, the only option is to restart the Mac. This may not be possible remotely without a network connection. Only special KVM hardware that brings its own network supply helps here.
Data centers where Macs have been placed as colocation, as well as long-running Mac clusters or rendering workstations, are likely also affected by the problem.
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