Windows 11 Update: Bug in .NET Framework Causes Apps to Crash


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

This is apparent from a new entry to Microsoft Support. With known issues documented by Microsoft in the Windows Release Health Dashboard, you can now find accurate information about the issue (via ONMSFT). Microsoft had just fixed the safe mode problems that appeared with the KB5012643 update. However, there is still no fix for the new bug. Instead, Microsoft recommends everyone affected to uninstall the update again.

Since this is an optional update, there’s always hope that there aren’t too many at the moment. Also, unlike the safe mode issue, Microsoft has not yet rolled back this issue as a known issue to roll users back to a bug-free version. The true extent of the problem is not known. The error appears in connection with applications that use components of the .NET 3.5 framework. The group did not disclose in detail the apps involved.

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

Microsoft support says:

  • Description error: Some .NET Framework 3.5 applications may experience issues
  • OS Version 22000.652 / KB5012643
  • After installing KB5012643, some .NET Framework 3.5 applications may experience issues or fail to open. Affected applications use some optional components in .NET Framework 3.5, e.g. For example, Windows Communication Foundation (WCF) and Windows Workflow (WWF) components.

  • circumvent: To alleviate this issue, you can uninstall KB5012643. To do this, click on the Start button, type and select Windows Update settings. In the Windows Update Settings window, select View update history, 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 fix 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 administrators can do this programmatically by using an elevated command prompt (run as administrator) and running the following commands:
    • dism /online /activate-feature /featurename:netfx3 /all
    • dism/online/enable feature/feature name: WCF-HTTP-Activation
    • dism /online /enable feature /featurename:WCF-NonHTTP-Activation
  • Platforms concerned:
  • Client: Windows 11, version 21H2

Windows 11 Frequently Asked Questions Instructions, tips and tricks
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Windows 11, Microsoft Windows 11, Windows 10 Successor, Windows 11 Logo, Windows 11 Wallpapers, Windows 11 Background

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