Windows 11 update: Bug in .NET Framework causes apps to crash

Microsoft warns of a new bug in Windows 11. The KB5012643 update, which was marked as optional and was released at the end of April, causes problems with apps that use certain components of the .NET 3.5 framework.

This emerges from a new entry at Microsoft Support. With the known problems that Microsoft has in the Windows Release Health-Dashboard documented, you can now find exact information about the problem (via ONMSFT). Microsoft had just fixed Safe Mode issues that had appeared with the KB5012643 update. However, there is still no solution for the new bug. Instead, Microsoft recommends that everyone affected uninstall the update again.

Since this is an optional update, there is still hope that there are not too many affected at the moment. Also, unlike the Safe Mode issue, Microsoft has not yet rolled back this issue as a known issue to bring users back to a bug-free version. How widespread the problem actually is is not known. The error appears in connection with applications that use components of the .NET 3.5 framework. The group has not disclosed which apps are involved in detail.

The error causes the applications to fail and crash. Microsoft has announced that it is working on a solution that will be made available as an update in one of the next versions.

Microsoft Support says:

Error Description: Some .NET Framework 3.5 applications may have problems
OS Build 22000.652 / KB5012643
After installing KB5012643, some .NET Framework 3.5 applications may experience problems or may not open. The affected applications use certain optional components in the .NET Framework 3.5, e.g. For example, the Windows Communication Foundation (WCF) and Windows Workflow (WWF) components.

bypass: To mitigate this problem, you can uninstall KB5012643. To do this, click the Start button, type and select Windows Update settings. In the Windows Update Settings window, select View update history, and then select Uninstall update. Locate KB5012643 in the list, select it, and then choose Uninstall.
If you are unable to uninstall KB5012643, you can also resolve this issue by re-enabling .NET Framework 3.5 and Windows Communication Foundation in Windows Features. For instructions, see Enabling .NET Framework 3.5 in Control Panel. Advanced users or IT admins can do this programmatically by using an elevated command prompt (run as administrator) and running the following commands: