Microsoft Windows 11 26H1 Update Version OS Build 28000.2956

KB5129194 for Windows 11, version 26H1 (OS Build 28000.2956) is an out-of-band update. It adds protections for CVE-2026-62721 and CVE-2026-85921 and fixes RDS, Hyper-V Plan9 sharing, and USB audio multichannel issues. Reference IDs: KB5124012, KB5125104.

• Adds protections for CVE-2026-62721, a Windows User-Mode Power Service (UMPS) elevation of privilege vulnerability.
• Adds protections for CVE-2026-85921, a Windows Secure Kernel Mode elevation of privilege vulnerability.

• Fixes Remote Desktop Services instability after KB5124012, including RDP connection and sign-in failures and unresponsive management tools.
• Fixes Hyper-V issues where Plan9 shared host folders did not appear or could not be accessed in Linux VMs managed by HCS.
• Fixes USB Audio Class 1.0 devices failing in multichannel modes such as 8-channel or 3D audio.
• Includes servicing stack update KB5125104 to improve Windows Update installation reliability.

• USB Audio Class 1.0 devices may fail to start or produce audio after the September 8, 2026 security update, showing Code 10, no output, or unresponsive sound settings. Microsoft says a resolution is in progress.

• If previous updates are already installed, only the new changes in this package will be downloaded and installed.
• AI components are updated to version 1.2608.951.0 for Image Search, Content Extraction, Semantic Analysis, and Settings Model.

• KB5129194 release notes
  https://support.microsoft.com/help/5129194

Product Information

Vendor: Microsoft

Product: Windows 11

Product type: Software

Application category: Utilities

Platform: Windows

Variant: 26H1

Version: OS Build 28000.2956

Vendor information published: Sep 14, 2026

Original release notes: View on vendor site

Published on updatealert.io: Sep 17, 2026

Description: Client operating system for modern desktop and enterprise environments.