KB5003254: Windows 10 Version 21H1

A new Cumulative Update is rolling out for .NET Framework 3.5 and 4.8. This .NET framework update is rolling out on Windows 10 Version 21H1 computers starting from June 8.

Microsoft has provided an official changelog for this KB5003254 update which can be read below.

The following quality and reliability improvements are included in the KB5003254:


  • 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.


  • 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.