Home SecurityOS Security The .NET patch failure that wasn’t

The .NET patch failure that wasn’t

When we started this month of patching, I fully expected to come back by now with massive listings of applications that hated the February updates. That hasn’t been the case, though there have been some issues related to .NET this month. 

In case you’re wondering, .NET is a framework used by developers to build applications. It makes for standard coding techniques and “managed code” and can make an app more secure. Developers primarily use Visual studio to develop software that we all use on our Windows systems.

Known issues affecting Visual Studio most dramatically appeared in updates first introduced with the cumulative .NET updates beginning last month. KB4598301 was released Jan. 26 as an optional preview update for .NET on Windows 10 1909 and caused Visual Studio to crash. Then KB4601056, released Feb. 9, suffered from the same issue. So Microsoft released a preview update a week later —  KB4601556 — that fixed the underlying issue in Win10 1909.

The Patch Tuesday release of KB4601887 for Windows 10 1809 was later fixed by KB4602298, though not for all platforms. For example, the release of KB4601050 for Windows 2004/20H2, KB4601054 for Win10 1803, and  KB4601051 for Win10 1607 were not fixed with later releases. I expect that for these platforms you’ll have to wait until the March updates arrive if you are seeing application crashes.

Otherwise, I’ve been surprised by how few reports of issues I’ve seen after these updates were installed. In my own personal testing, I have not seen issues — though there have been reports of problems from other users. One report involves Autodesk’s Inventor 2020 and 2021, which crashes with these updates installed. But application crashes have been few and far between; thus, I don’t anticipate you will have issues this month.

Another report I’ve seen comes from the VMware forum, where this patch was installed on Server 2016 deployments and blocked the ability to fully enroll iOS devices with Intelligent Hub 21.01. As the VMware knowledge base notes, several .NET updates released in February cause issues with Workspace ONE UEM functionality including secure channel communication.

As noted on the VMware page, all of the following .NET patches trigger this issue:

I personally have not seen any impact on one of my key applications built on .NET: Intuit’s QuickBooks. Neither the 2018, 2019, 202,0 or the 2021 versions of QuickBooks have had issues.

The good news is that the security issue fixed in these patches merely blocks an attacker from performing a denial of service. Ironically, since the patch makes the application crash, it effectively causes the same thing it’s trying to protect users from. If you must remove this update, I don’t see it as a high risk if you can’t install it at this time.

Because I haven’t seen many reported side effects (including in my own testing), next week I’ll be recommending you install the updates the Feb. 9 batch of patches unless you are directly impacted by the .NET update. Based on my review of the patch forums and venues, I’ve only seen side effects with certain business apps. The issues have been narrow and not wide spread. That’s the good news.

If you find you do need to uninstall the update, you’ll face a two step process. First, go to Start button, then Settings, then Update and security. Click on view update history and then on “Uninstall updates.”

uninstall updates Microsoft

Scroll down and find the Update for Microsoft Windows with the matching KB number that corresponds with the version of Windows 10, 8 or 7 you have. For Windows 10, for example, you’ll need to look for one of the following:

  • Windows 10 version 1607 – KB4601051
  • Windows 10 version 1809 – KB4601887
  • Windows 10 version 1909 – KB4601056
  • Windows 10 version 2004 or 20H2 – KB4601050

Now comes the harder part: Especially for Windows 10, you’ll need to ensure that you set your system so it will not reinstall this update if you have been impacted. First, download the WUSHOWHIDE.DIAG tool from Oldergeeks.com and install it. (As you may recall from my last blog post, this tool is no longer available from Microsoft.) Now, look for the update you wish to hide or block from installing and select it.


Click on show or hide updates and then select to hide the .NET update and click next.

Wushowhide detailsWushowhide

The application will indicate that application is “resolving” problems and will hide the update from being offered up to your system. An alternative tool is Windows Update Minitool, which allows you to hide updates as well.

For many years I’ve been wary of .NET updates and would cringe when they were released. There were many years we’d have to use various .NET repair tools to uninstall and reinstall .NET. Since Microsoft released .NET 4.8 and later, and included it in Windows 10, it’s become much better behaved — meaning we have not needed to uninstall and manually reinstall .NET. This is one of the first times I can recall that a .NET update has gone out with a known issue in a long while.

Bottom line, the big patching issue I thought would occur has been isolated. Thankfully, this time .NET has been generally well behaved; it hasn’t (yet) caused me to wince and cringe.  

Copyright © 2021 IDG Communications, Inc.

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