Microsoft Exchange stopped delivering email on 1 January 2022

transcript

1 January 2022. Exchange servers stop delivering email. Because of one number. And the new year.

Exchange has a built-in malware scanner. It downloads signature updates. Admins open the logs. Can't convert 2201010001. The engine won't load. Mail piles up in the queues.

The villain? A security researcher spelled it out. The version held a date, in a signed 32-bit integer. Its limit is about 2 point 1 billion. Versions starting 21 fit. The 2022 value starts 22. About 2 point 2 billion. Too big.

A new update arrives. The engine checks its version. The number doesn't fit. The engine crashes. No scan, no delivery. Mail just sits there.

Some admins switch malware filtering off. Mail flows. Unprotected. Microsoft's fix: a script. Wipe the engine, download a fresh one. Customers had to run it. On every affected server.

And the version you get after the fix? 2112330001. Read it as a date. 21, 12, 33. December the 33rd, 2021.

Pack a date into a number. Now the number expires. Test your clock forward. Before the calendar does it for you.

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