KB5012643 for Windows 11 may crash some .Net apps


Microsoft released the preview update KB5012643 for Windows 11 on April 25, 2022. Preview updates are not installed automatically via Windows Update; Microsoft uses the previews to test the updates and fix potential issues that come up through user reports or Telemetry data.

windows 11 KB5012643 app crash issue

It appears that the April 2022 preview update for Windows 11 is causing issues with certain .NET Framework applications after it is installed on devices.

An entry under known issues provides the following information to IT administrators:

After installing this update, some .NET Framework 3.5 apps might have issues or might fail to open. Affected apps are using certain optional components in .NET Framework 3.5, such as Windows Communication Foundation (WCF) and Windows Workflow (WWF) components.

The issue appears limited to certain applications that use optional .NET Framework 3.5 components. Microsoft does not provide examples of such applications, but users may notice crashes or other issues when launching affected applications on Windows 11 devices.

Microsoft suggests two mitigations to deal with the issue:

  1. Remove the Windows update KB5012643 from the device. Administrators may do so in the following way:
    • Open Start and type Windows Update Settings.
    • Select View Update History and then Uninstall Update.
    • Locate KB5012643 in the list, select it, and then activate the uninstall action.
  2. Re-enable .NET Framework 3.5 and the Windows Communication Foundation in Windows Features. IT administrators may run the following comments from an elevated command prompt window to do so:
    • dism /online /enable-feature /featurename:netfx3 /all
    • dism /online /enable-feature /featurename:WCF-HTTP-Activation
    • dism /online /enable-feature /featurename:WCF-NonHTTP-Activation

Microsoft plans to release a fix in “an upcoming update”. It is unclear if this could be in next week’s Patch Day updates of May 2022, or if the issue will be fixed in a future update.

Windows 10 preview updates do not appear to cause the issue on systems they are installed on.

Closing Words

Preview updates, which Microsoft releases at the end of every month, are beta updates. I recommend to install preview updates only if they address a major issue that is experienced on a device, otherwise, it may be better to wait for the final release on the next Patch Day.

It is possible that the issue will still be present in the coming May 2022 Patch Day update; if that is the case, users may address the issue by following Microsoft’s suggestions listed above.

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