February 9, 2021-KB4601051 Cumulative Update for .NET Framework 4.8 for Windows 10, version 1607 and Windows Server, version 2016
Release Date:
February 9, 2021Version:
.NET Framework 4.8Summary
Security Improvements
This security update addresses a denial of service vulnerability in .NET Framework. For more information please see CVE-2021-24111.
Quality 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%. |
CLR |
- Improves the reliability of automatic Native Image generation task. |
1 Windows Presentation Foundation (WPF)
Known issues in this update
Symptom |
After installing this update, WPF apps may crash with a callstack similar to
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:
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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 1607 and Windows Server, version 2016 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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Protect yourself online: Windows Security support
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Learn how we guard against cyber threats: Microsoft Security