Yesterday, we released the May 2021 Security and Quality Rollup Updates for .NET Framework.

Quality and Reliability

This release contains the following quality and reliability improvements.

CLR¹

• Addresses an issue where the entire process would be torn down when a NullReferenceException propagated out of an exception filter.
• Addresses an issue with slowdowns that could occur when making large numbers of devirtualized calls into MarshalByRefObject-derived code.

Windows Forms

• Addresses an issue in ComboBox drop down item bounding rectangle as exposed to the accessibility tools, where we did not take into account that some items might be scrolled out of view, we had always started counting items from the first visible one, and thus item rectangle location was incorrect.
• Implemented ScrollItemPattern (IScrollItemProvider (uiautomationcore.h) – Win32 apps | Microsoft Docs) for ComboBox drop down items.

WPF²

• Addresses an issue with lag responding to typing in TextBox, when spell-checking is enabled that was introduced in an update earlier this year.
• Addresses an issue with a leak of touch-related resources, including OS handles, when closing a window. The leak only occurs when a touch device is active, and only for windows whose HwndSource is created directly by the app.
• Addresses a crash when docking a window within Visual Studio, or, more generally, disposing an HwndSource whose RootVisual is null.

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

Getting the Update

The Security and Quality Rollup is available via Windows Update, 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+ versions.

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

Previous Monthly Rollups

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

• .NET Framework February 2021 Cumulative Update Preview for Windows 10 2004, Windows Server, version 2004, Windows 10, version 20H2 and Windows Server, version 20H2
• .NET Framework February 2021 Cumulative Update Preview for .NET Framework.
• .NET Framework February Security and Quality Rollup
• .NET Framework January Security and Quality Rollup Update