February 9, 2021-KB4601056 Cumulative Update for .NET Framework 3.5 and 4.8 for Windows 10, version 1909, and Windows Server, version 1909

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Release Date:
February 9, 2021

Version:
.NET Framework 3.5 and 4.8

Summary

This security update addresses a denial of service vulnerability in .NET Framework. For more information please see CVE-2021-24111.

Known issues in this update

Symptom

After installing this update, WPF apps may crash with a callstack similar to

Exception Info: System.NullReferenceException at System.Windows.Interop.HwndMouseInputProvider.HasCustomChrome(System.Windows.Interop.HwndSource, RECT ByRef)
at System.Windows.Interop.HwndMouseInputProvider.GetEffectiveClientRect(IntPtr)
at System.Windows.Interop.HwndMouseInputProvider.PossiblyDeactivate(IntPtr, Boolean)
at System.Windows.Interop.HwndMouseInputProvider.Dispose()

This occurs when disposing an HwndSource whose RootVisual is null, a situation that arises in Visual Studio when docking or splitting windows, and could arise in other apps.

Workaround

This issue is resolved in KB4601556.

How to get this update

Install this update

Release Channel

Available

Next Step

Windows Update and Microsoft Update

Yes

None. This update will be downloaded and installed automatically from Windows Update.

Microsoft Update Catalog

Yes

To get the standalone package for this update, go to the Microsoft Update Catalog website.

Windows Server Update Services (WSUS)

Yes

This update will automatically sync with WSUS if you configure Products and Classifications as follows:

Product: Windows 10, version 1909, and Windows Server, version 1909

Classification: Security Updates

File information

For a list of the files that are provided in this update, download the file information for cumulative update.

Information about protection and security

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