Microsoft recently released monthly Windows 11 update KB5012643 to Windows 11 running PCs. The update brings a new feature & many security improvements for windows components. But Windows 11 update KB5012643 is also breaking Safe Mode and failing to install for many users. These issues have been reported in official Microsoft forum by many Windows 11 users.

KB5012643 fails to install for many:

Many Users have reported 1, 2, 3 that the update KB5012643 fails to install for them. The update download gets stuck and doesn’t install further for some, while some users don’t succeed in installing it after downloading.

KB5012643 will not completely download and install

I am on Windows 11 and KB5012643 will not download past 51 %. I have run the Windows Update Troubleshooter, a problem was detected and fixed. But the KB is NOT completely downloaded and installed. Would appreciate any help to fix this problem. Thanks.

Windows 11 Cumulative Update not downloading and installing.

2022-04 Cumulative Update for Windows 11 for x64-based Systems (KB5012643) not downloading.

KB5012643 Update Installation problem

ImageNot able to install update KB5012643 neither from windows update nor from windows update catalogue

KB5012643 breaks Safe Mode:

After installing update KB5012643, the issue of broken Safe mode has been reported in a thread at the Microsoft Forum.

KB5012643 Breaks Safe-Mode

Hi – After installing KB5012643 I have found that going into Safe-Mode is broken and the screen just flashes up random windows.

Has anyone else seen this problem with Safe-Mode after KB5012643 is installed?

In the same thread many other users have confirmed the issue.

Hi Billy, I just tested this and safe mode is horribly broken. The eventlog shows many services as not being able to start, it also seems like Windows Explorer is stuck in a crash loop. If I figure out anything more, I’ll post back.

I’m experiencing the exact same issue. You are locked in a loop where windows explorer is constantly restarting. I was able to get out from there by open a Task Manager -> File -> Run new task. But then again you have to run the msconfig and select a normal start up between the loop cycles which is hilarious.

Same here, safe mode crash loop. Uninstalling KB5012643 helped.

I used msconfig to enable safe mode, so to disable it had to work a hard with win+R + enter (since it used last entered value – msconfig). At some ~200 time screen stayed on top and wasn’t closed 😀

In event logs I see a lot of errors every second:

DCOM got error “1084” attempting to start the service WpnUserService_3c042 with arguments “Unavailable” in order to run the server: