Microsoft Support:
The September 8, 2026 update for Windows 11, version 26H1 includes security and cumulative reliability improvements in .NET Framework 4.8.1. We recommend that you apply this update as part of your regular maintenance routines. Before you install this update, see the Prerequisites and Restart requirement sections.
Summary
Security ImprovementsCVE-2026-62886 - .NET Framework Elevation of Privilege vulnerability
This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-62886.
CVE-2026-69522 - .NET Framework Remote Code Execution vulnerability
This security update addresses a remote code execution vulnerability detailed in CVE-2026-69522.
Quality and Reliability Improvements
| NET Fundamentals | - Addresses an issue where intermittent crashes could occur in some 64-bit .NET Framework scenarios. |
Known issues in this update
Microsoft is not currently aware of any issues in this update.How to get this update
Install this update| Release Channel | Available | Next Step |
|---|---|---|
| Windows Update and Microsoft Update | Yes | None. This update will be downloaded and installed automatically from Windows Update. |
| Windows Update for Business | Yes | None. This update will be downloaded and installed automatically from Windows Update. |
| Microsoft Update Catalog | Yes | To get the standalone package for this update, go to the Microsoft Update Catalog website. |
| Windows Server Update Services (WSUS) | Yes | This update will automatically sync with WSUS if you configure as follows: Product: Windows 11, version 26H1 Classification: Security Updates |
File information
For a list of the files that are provided in this update, download the file information for cumulative update.
Prerequisites
To apply this update, you must have .NET Framework 4.8.1 installed.Restart requirement
You must restart the computer after you apply this update if any affected files are being used. We recommend that you exit all .NET Framework-based applications before you apply this update. Source:
September 8, 2026-KB5126053 Cumulative Update for .NET Framework 4.8.1 for Windows 11, version 26H1 | Microsoft Support
September 8, 2026-KB5126053 Cumulative Update for .NET Framework 4.8.1 for Windows 11, version 26H1
support.microsoft.com
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