.NET Framework May 2021 Cumulative Update Preview for Windows 10, versions 2004, 20H2, 21H1

Tara Overfield

Today, we are releasing the May 2021 Cumulative Update Preview for .NET Framework.

Quality and Reliability

This release contains the following quality and reliability improvements.

  • Addresses a performance issue caused by incorrect configuration in the GC.
  • Addresses an issue where a background GC could pause the runtime for a long period of time if a large managed heap is filled with long lived objects with a deep chain of references.
  • Addresses an issue where crashes could occur if security stackwalks were generated during ThreadAbortException handling.
  • .NET Framework 4.8 will now allow to negotiate TLS 1.3 if underlying OS supports it.
  • Addresses an issue when rapid typing using an IME can crash via FailFast.
  • Addresses an issue where Thaana characters displayed in left-to-right order.
  • Addresses a crash when WebBrowser receives a completion event for a navigation it tried to cancel.

1 Common Language Runtime (CLR) 2 Network Class Library (NCL) 3 Windows Presentation Foundation (WPF)

Getting the Update

The Cumulative Update Preview is available via Windows Update and Microsoft Update Catalog.

Microsoft Update Catalog

You can get the update via the Microsoft Update Catalog. Customers that rely on Windows Update 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 2019+ versions.

Product Version Cumulative Update
Windows 10 Version 21H1
.NET Framework 3.5, 4.8 Catalog 5003254
Windows 10, version 20H2 and Windows Server, version 20H2
.NET Framework 3.5, 4.8 Catalog 5003254
Windows 10 2004 and Windows Server, version 2004
.NET Framework 3.5, 4.8 Catalog 5003254


Previous Monthly Rollups

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

1 comment

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  • Vadim Sterkin 0


    Can you explain why we’re getting the preview .NET updates downloaded and installed automatically and waiting for restart?

    This is:
    • a non-managed 19043.985, which is not an insider build
    • not a seeker experience, that is we don’t check for updates manually
    • not a single incident on a single machine, that is “we” means multiple people are affected, and not just with this May preview update

    Note that on the same picture the LCU preview is waiting to download and install. That’s a pretty typical picture at the end of every month. So why don’t you respect the “simple and predictable” Windows 10 servicing cadence? I mean this https://techcommunity.microsoft.com/t5/windows-it-pro-blog/windows-10-update-servicing-cadence/ba-p/222376


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