Microsoft: Windows 11 KB5012643 update will break some apps

Windows

Microsoft has warned Windows 11 users that they might experience issues launching and using some .NET Framework 3.5 applications.

This known issue impacts only systems running Windows 11, version 21H2, where users have installed the KB5012643 optional preview cumulative update.

Affected apps use optional components such as Windows Workflow (WWF) and Windows Communication Foundation (WCF).

"After installing KB5012643, some .NET Framework 3.5 apps might have issues or might fail to open," Microsoft revealed on the Windows health dashboard.

The company also addressed another known issue triggered after installing this Windows non-security update, leading to flickering screen problems in Safe Mode without Networking.

The same KB5012643 issue also made some Windows apps (e.g., File Explorer, Start Menu, and Taskbar) seem unstable while running in Safe Mode.

Workaround available for affected systems

Microsoft asked impacted users to uninstall the problematic KB5012643 update to work around this issue and restore their .NET Framework 3.5 apps' functionality.

You have to open the Windows Update settings window by searching for Windows Update in the Start menu.

From there, you need to click View Update History, hit Uninstall Update, then click "Uninstall" after selecting the KB5012643 update the list.

Those who cannot immediately uninstall this cumulative update can mitigate the known issue by re-enabling .NET Framework 3.5 and the Windows Communication Foundation from the Windows Features dialog.

IT admins and advanced users can also do this via an elevated Command Prompt (launched as administrator) by running these commands:

dism /online /enable-feature /featurename:netfx3 /all
dism /online /enable-feature /featurename:WCF-HTTP-Activation
dism /online /enable-feature /featurename:WCF-NonHTTP-Activation

Microsoft is currently working on a resolution to address this issue and will provide an update with an upcoming release.

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Microsoft: Windows 11 KB5012643 update will break some apps