Update: Microsoft Update KB5066835 blocks Lights-Out
Unfortunately, the Microsoft update KB5066835 from October 2025 has unpleasant side effects on HttpListener, which is also used by Lights-Out on the server.
Who is affected?
All users who operate a Windows 11 computer as a server with Lights-Out. It is not possible to log in, either from the clients or via the console.
Solution 2
As of today, October 16, 2025 Microsoft published KB2267602 (Security Intelligence Update for Microsoft Defender Antivirus). Please re-enable automatic updates! After installation a reboot is required to make everything work again.
Solution 1
As of today, October 15, 2025, there is no workaround.
The only solution is to uninstall KB5066835 and, if necessary, KB5065789 (preview version) and, importantly (!), to then suspend updates for 2-4 weeks.
To uninstall, either use the UI or run these two commands in a terminal:
wusa /uninstall /kb:5066835
wusa /uninstall /kb:5065789A reboot is required after uninstallation!
This blog article will be updated if there are any new findings.
