HN · HACKER_NEWS// 5d agoNEWS

macOS TCP stack fails after 49.7 days

A 32-bit integer overflow in the macOS kernel's tcp_now variable causes the network stack to stop accepting new TCP connections after approximately 49.7 days of system uptime. While the system appears functional and continues to respond to ICMP pings and UDP traffic, the TCP state machine incorrectly identifies new packets as stale, effectively severing most internet and local network connectivity until a full reboot is performed.

// ANALYSIS

The "49.7-day wall" is a classic technical debt symptom surfacing in a modern operating system.

–The overflow of the 32-bit millisecond counter is identical to the famous Windows 95 crash bug.
–Selective failure of TCP while UDP/ICMP remain active makes it a "silent killer" for diagnostic tools.
–Affects both Intel and Apple Silicon, though the specific hardware sleep behavior can delay the onset.
–Rebooting resets the counter, but a formal kernel patch from Apple is required for long-term server/workstation stability.
–Highlights the importance of 64-bit timestamps even for internal kernel networking clocks.

// TAGS

macosnetworkingtcpkernelinfrastructure

DISCOVERED

5d ago

2026-04-07

PUBLISHED

5d ago

2026-04-06

RELEVANCE

5/ 10

AUTHOR

RyanZhuuuu