KB5012643 for Windows 11 may crash some .Net apps

Martin Brinkmann
May 4, 2022
Windows 11 News

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.

Now You: do you run .NET applications?

KB5012643 for Windows 11 may crash some .Net apps
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KB5012643 for Windows 11 may crash some .Net apps
The preview update KB5012643 may cause .NET Framework application crashes or issues on Windows 11 devices it is installed on.
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  1. Grandma Says Just Say NO! said on May 5, 2022 at 9:10 am

    Yet still another reason why Windows is not ready for the desktop.

    What, you expect Grandma to sort out all of these problems with the OS and workarounds?

  2. Anonymous said on May 5, 2022 at 4:54 am

    People still use Windows 11?

  3. semce2 said on May 4, 2022 at 10:41 pm

    I installed it on my laptop and didn’t experience any issues. It did fix a previous issue that when I connected to internet with my vpn, Windows showed no internet connection, even though Firefox had no problem browsing the internet. Some other apps would show no internet connection but Windows update worked as usual. Anyway, fixed now it seems.

  4. dmacleo said on May 4, 2022 at 4:55 pm

    I installed it on one machine and have not seen any issues.
    essentials servers still use 3.5 on client machines and my daily backups, remote access, etc still ok.
    this was not in WSUS but I installed on one machine to test so that when hits WSUS I would know if I should decline or push to the 4 win11 clients on this (small) domain.

  5. John G. said on May 4, 2022 at 2:57 pm

    This update is a complete nightmare, and it’s still available at MS servers to continue its painful disasters around the world. In fact I can’t install it because it gives error 0x80070005 and after applied W11 fixing update tool it gives error 0x80248014. First installation broke W11 and I needed to fix it with DISM and SCF, however the system was unstable all day long so I finally ought to restore a security backup point to get my system fine again. Second installation again failed, and also the same broken system was obtained. If installed through Windows Catalog it also fails with no mercy. And it still appears the advice that KB5012643 has been not installed and that I can download it again to reinstall. Ubuntu updates are so good that they are some lightyear distance far from W11 ones. Thanks for the article! :]

    1. Frankel said on May 4, 2022 at 5:16 pm

      I’m sure rolling back a clonezilla image takes about 10 minutes on an NVME or SSD. There is no real reason for professionals here to complain about botched updates in beta and alpha channels if the issues are self-caused and not mitigated with the default cure-it-all tools.

      1. John G. said on May 4, 2022 at 8:41 pm

        @Frankel this update is offered as optional through the windows update system, so I installed it because it has in theory some good error fixes. However it has several bad issues. Removing it’s not enough, I have to restore a backup point because DISM and SFC didn’t work.

      2. Frankel said on May 4, 2022 at 8:53 pm

        I don’t blame you for installing, I do install optional updates too, in hope of even receiving security fixes a few days earlier. I just think you are professional enough to prepare yourself for potential fallout. Windows tools are notoriously unreliable.

      3. John G. said on May 5, 2022 at 12:18 am

        @Frankel since few minutes ago this optional update is no longer available! Probably MS is getting ready for tuesday 10th, may updates. I hope the upcoming update will be good. :]

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