Release Date:January 26, 2021

Version:.NET Framework 3.5 and 4.8

The January 26, 2021 update for Windows 10, version 1809 and Windows Server, version 2019 includes cumulative reliability improvements in .NET Framework 3.5 and 4.8. We recommend that you apply this update as part of your regular maintenance routines. Before you install this update, see the Prerequisite and Restart requirements sections.

Quality and reliability improvements

ASP.NET

- Addresses an issue where after installing the update released on October 20th, some ASP.Net applications fail during precompilation – likely with a message that contains the words “Error ASPCONFIG.”

WPF1

- Addresses a hang when scrolling to the end of a TreeView, when layout rounding is enabled and DPI scaling is not 100%.

CLR2

- Improves the reliability of automatic Native Image generation task.

1 Windows Presentation Foundation (WPF)2 Common Language Runtime (CLR)

Known issues with 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

To work around this problem, set two AppContext switches using one of the methods described in AppContext Class (System) under the heading “AppContext for library consumers”.  The switches are named Switch.System.Windows.Interop.MouseInput.OptOutOfMoveToChromedWindowFix and Switch.System.Windows.Interop.MouseInput.DoNotOptOutOfMoveToChromedWindowFix and both should be set to “true”.   The first switch avoids the crash, but re-introduces the bug fixed in the KBs.  The second switch is currently ignored, but will be recognized in a future .NET update that contains a fix for the null-reference crash;  it restores the original bug fix.

For example, using the app.config file method to apply the workaround at application scope:

<AppContextSwitchOverrides value="Switch.System.Windows.Interop.MouseInput.OptOutOfMoveToChromedWindowFix=true; Switch.System.Windows.Interop.MouseInput.DoNotOptOutOfMoveToChromedWindowFix=true " />

Additional information about this update

The following articles contain additional information about this update as it relates to individual product versions.

  •  4598461 Description of the Cumulative Update for .NET Framework 3.5, 4.7.2 and 4.8 for Windows 10, version 1809 and Windows Server, version 2019 (KB4598461)

How to get this update

Install this update

Release Channel

Available

Next Step

Windows Update and Microsoft Update

Yes

To download and install this update, go to Settings > Update & Security > Windows Update, and then select Check for updates.

Microsoft Update Catalog

Yes

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

Windows Server Update Services (WSUS)

No

You can import this update into WSUS manually. See the Microsoft Update Catalog for instructions.

Note: This update is available on WSUS via 4598461.

File information

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

Prerequisites

To apply this update, you must have .NET Framework 3.5 or 4.8 installed.

Restart requirement

You must restart the computer after you apply this update if any affected files are being used. We recommend that you exit all .NET Framework-based applications before you apply this update.

How to obtain help and support for this update

Facebook LinkedIn E-post

Trenger du mer hjelp?

Vil du ha flere alternativer?

Discover Community

Explore subscription benefits, browse training courses, learn how to secure your device, and more.

Microsoft 365 subscription benefits

Microsoft 365 training

Microsoft security

Accessibility center

Communities help you ask and answer questions, give feedback, and hear from experts with rich knowledge.

Ask the Microsoft Community

Microsoft Tech Community

Windows Insiders

Microsoft 365 Insiders