.NET Framework February Security and Quality Rollup

Tara Overfield


Revised 4/15/2021: On April 13th, 2021, this update was released to replace a previous release of this some updates. See known issues section for more details. If you’ve already installed a previous release of an affected update, no action is required.

Today, we are releasing the February 2021 Security and Quality Rollup Updates for .NET Framework.


CVE-2021-24111– .NET Framework Denial of Service Vulnerability

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

Quality and Reliability

This release contains the following quality and reliability improvements.

  • 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.”
  • Improves the reliability of automatic Native Image generation task.
  • Addresses a hang when scrolling to the end of a TreeView, when layout rounding is enabled and DPI scaling is not 100%.

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

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 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


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:

Switch.System.Windows.Interop.MouseInput.DoNotOptOutOfMoveToChromedWindowFix=true " />
Resolution For some Windows 10, version 1809, Windows Server 2019 and newer versions this issue is resolved in February 2021 Cumulative Update Preview


Symptom Customers using Windows 7 SP1, Windows Server 2008 R2 SP1 or Windows Server 2008, this update does not install, and it returns either or both of the following error messages:

  • -2146762495
  • A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file.

This issue was corrected by the latest release of this update.  If you’ve already installed a previous release of this update, no action is required.

Getting the Update

The Security and Quality Rollup is available via Windows Update, Windows Server Update Services, and Microsoft Update Catalog. The Security Only Update is available via Windows Server Update Services and Microsoft Update Catalog.

Microsoft Update Catalog

You can get the update via the Microsoft Update Catalog. For Windows 10, NET Framework 4.8 updates are available via Windows Update, Windows Server Update Services, Microsoft Update Catalog. Updates for other versions of .NET Framework are part of the Windows 10 Monthly Cumulative Update.

**Note**: Customers that rely on Windows Update and Windows Server Update Services will automatically receive the .NET Framework version-specific updates. Advanced system administrators can also take use of the below direct Microsoft Update Catalog download links to .NET Framework-specific updates. Before applying these updates, please ensure that you carefully review the .NET Framework version applicability, to ensure that you only install updates on systems where they apply.

The following table is for Windows 10 and Windows Server 2016 and newer versions.

Product Version Cumulative Update
Windows 10, version 20H2 and Windows Server, version 20H2
.NET Framework 3.5, 4.8 Catalog 4601050
Windows 10 2004 and Windows Server, version 2004
.NET Framework 3.5, 4.8 Catalog 4601050
Windows 10 1909 and Windows Server, version 1909
.NET Framework 3.5, 4.8 Catalog 4601056
Windows 10 1809 (October 2018 Update) and Windows Server 2019 4601887
.NET Framework 3.5, 4.7.2 Catalog 4601060
.NET Framework 3.5, 4.8 Catalog 4601055
Windows 10 1803 (April 2018 Update)
.NET Framework 3.5, 4.7.2 Catalog 4601354
.NET Framework 4.8 Catalog 4601054
Windows 10 1703 (Creators Update)
.NET Framework 3.5, 4.7, 4.7.1, 4.7.2 Catalog 4601330
.NET Framework 4.8 Catalog 4601052
Windows 10 1607 (Anniversary Update) and Windows Server 2016
.NET Framework 3.5, 4.6.2, 4.7, 4.7.1, 4.7.2 Catalog 4601318
.NET Framework 4.8 Catalog 4601051

The following table is for earlier Windows and Windows Server versions.

Product Version Security and Quality Rollup Security Only Update
Windows 8.1, Windows RT 8.1 and Windows Server 2012 R2 4603004 4602960
.NET Framework 3.5 Catalog 4578953 N/A N/A
.NET Framework 4.5.2 Catalog 4578956 N/A N/A
.NET Framework 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2 Catalog 4601048 Catalog 4601094
.NET Framework 4.8 Catalog 4601058 Catalog 4601092
Windows Server 2012 4603003 4602959
.NET Framework 3.5 Catalog 4578950 N/A N/A
.NET Framework 4.5.2 Catalog 4578954 N/A N/A
.NET Framework 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2 Catalog 4600957 Catalog 4601093
.NET Framework 4.8 Catalog 4601057 Catalog 4601091
Windows 7 SP1 and Windows Server 2008 R2 SP1 4603002 4602958
.NET Framework 3.5.1 Catalog 4578952 N/A N/A
.NET Framework 4.5.2 Catalog 4578955 N/A N/A
.NET Framework 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2 Catalog 4600945 Catalog 4601090
.NET Framework 4.8 Catalog 4600944 Catalog 4601089
Windows Server 2008 4603005 4602961
.NET Framework 2.0, 3.0 Catalog 4578951 N/A N/A
.NET Framework 4.5.2 Catalog 4578955 N/A N/A
.NET Framework 4.6 Catalog 4600945 Catalog 4601090


Previous Monthly Rollups

The last few .NET Framework Monthly updates are listed below for your convenience:


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