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

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.

This blog article will be updated if there are any new findings.