KB5082420: Cumulative Update for .NET Framework 3.5 and 4.8.1 - Windows 11 24H2 (April 2026)

Summary

This is a security and cumulative reliability update for .NET Framework 3.5 and 4.8.1 on Windows 11, version 24H2, released by Microsoft Support on April 14, 2026. Classified as a Security Update, it patches six CVEs and resolves a Windows Communication Foundation (WCF) reliability issue. Microsoft recommends applying it as part of regular maintenance.

Improvements and fixes

• Patches CVE-2026-32178, a remote code execution vulnerability in .NET Framework.
• Patches CVE-2026-32203, a denial-of-service vulnerability in .NET Framework.
• Patches CVE-2026-32226, a second denial-of-service vulnerability in .NET Framework.
• Patches CVE-2026-23666, a third denial-of-service vulnerability in .NET Framework.
• Patches CVE-2026-26171, a security feature bypass vulnerability in .NET Framework.
• Patches CVE-2026-33116, an information disclosure vulnerability in .NET Framework.
• Resolves an issue that prevented a WCF NamedPipe service from running correctly inside a Win32 app container on Windows 11 or Windows Server 2025.

Known issues

Microsoft lists no known issues for this update at the time of writing.

How to get this update

This update is available through multiple delivery channels. No additional steps are needed for Windows Update and Windows Update for Business - the update downloads and installs automatically. For WSUS, configure the product as Windows 11, version 24H2 and the classification as Security Updates to ensure the update syncs. A standalone package is available from the Microsoft Update Catalog for environments that require manual deployment.

Prerequisites: .NET Framework 3.5 or 4.8.1 must already be installed on the target machine.

Restart requirement: A restart is required after applying this update if any of the affected files are in use at install time. Microsoft recommends closing all .NET Framework-based applications before beginning installation.

Frequently asked questions

Does this update apply to both .NET Framework 3.5 and 4.8.1 simultaneously?

Yes. KB5082420 is a single cumulative update that covers both .NET Framework 3.5 and 4.8.1 on Windows 11, version 24H2. Applying it once addresses the documented security vulnerabilities and the WCF reliability fix across both framework versions on the same machine.

Will this update install automatically, or do I need to deploy it manually?

For endpoints managed through Windows Update, Microsoft Update, or Windows Update for Business, the update downloads and installs without administrator intervention. For WSUS-managed environments, you must confirm the product and classification settings are correct before the update appears for approval and deployment.

Is a restart always required after installing this update?

A restart is required only if files being replaced are currently in use. To reduce the likelihood of a forced restart, Microsoft recommends exiting all .NET Framework-based applications before applying the update. Planning the install during a standard maintenance window is advisable to avoid unexpected service interruptions.

What is the WCF NamedPipe fix included in this update?

The update addresses a reliability issue where a Windows Communication Foundation (WCF) NamedPipe service failed to run correctly when hosted inside a Win32 app container on Windows 11 or Windows Server 2025. No workaround is documented by Microsoft; applying this update is the resolution.