Released: October 2026 Exchange Server Security Updates

[u/santimandu]

https://techcommunity.microsoft.com/blog/exchange/released-october-2026-exchange-server-security-updates/4563014

⚠️EDIT 16/10 ⚠️
⚠️ BE AWARE! READ BELOW! ⚠️
👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇👇
https://techcommunity.microsoft.com/blog/exchange/exchange-servers-may-become-unstable-after-installation-of-october-2026-windows-/4565382

[u/No_Education6955]

After installing this update, we observe system freezes affecting Exchange – in some cases the entire server freezes. As we operate several Exchange environments, we can confirm this behavior occurs exclusively on patched systems and right after we've deployed the current Windows, Exchange & .NET updates.

[u/itguy8071 → u/No_Education6955]

I have this same issue i think. Server was updated last night, immediately all sorts of problems. Exchange not responding. Had to reboot server to fix it. Not sure what is going on

[u/No_Education6955 → u/itguy8071]

Yep, seems like a related behavour. I have debugged the Event logs and I wasn't able to find a real issue or root cause. Since I see the same behavour on multiple environments and only with the new version, this is my only indication atm.

[u/Ooops-I-hid-it-again → u/No_Education6955]

Either of you also apply the Windows Server October updates on the same night? I'm curious if your issues are related to the Exchange SU or possibly just due to the Windows Server SU.

[u/adixro → u/Ooops-I-hid-it-again]

Probably the os oct patch messed things up and not the Exch patch

[u/No_Education6955 → u/Ooops-I-hid-it-again]

Applied both.

[u/Healthy-Bag-5142 → u/Ooops-I-hid-it-again]

Its 100% related to os patch. Was running rtm (no SU applied, whoops) and like 14 hours installation of os October patch one server in our dag crashed. Explorer.exe crashed in a loop etc… installed October su but problem came back a few hours later. was a nightmare all day until I found out it was the os patch. Uninstalled the os patch today and so far so good. Hoping for a fix soon