.NET Framework May 2021 Cumulative Update Preview

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 1909
.NET Framework 3.5, 4.8 Catalog 5003256
Windows 10 1809 (October 2018 Update) and Windows Server 2019 5003396
.NET Framework 3.5, 4.7.2 Catalog 5003258
.NET Framework 3.5, 4.8 Catalog 5003255


Previous Monthly Rollups

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

1 comment

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  • Mystery Man 0

    Why is your “May 2021 Update” digitally signed on 9 April 2021?

    By the way, your previous “May 2021 Update” (KB4601554) was digitally signed on 11 February 2021. Windows 10 refused to install it since it contained nothing of value.

    See this: Cumulative blunder for .NET Framework!

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