KB5129195: Overview with user sentiment and feedback

Overview

KB5129195 is an out-of-band (OOB) emergency security update released on September 14, 2026, for Windows 11 versions 24H2 and 25H2 (OS Builds 26100.9457 and 26200.9457). This cumulative update addresses critical issues introduced by the September 2026 Patch Tuesday update (KB5124008) and includes security protections for CVE-2026-62721, a Windows User-Mode Power Service elevation of privilege vulnerability. The update was deployed urgently to resolve widespread functionality problems affecting Remote Desktop Services, audio devices, and virtualization features.

General Purpose

• Addresses CVE-2026-62721 security vulnerability in Windows User-Mode Power Service (UMPS) that could allow privilege escalation
• Resolves Remote Desktop Services (RDS) instability issues that prevented RDP connections and caused sign-in failures
• Fixes Hyper-V Plan9 folder sharing problems affecting HCS-managed virtual machines with Linux guests
• Partially resolves USB Audio Class 1.0 multichannel audio issues (8-channel and 3D audio modes)
• Restores functionality to Claude Cowork and other WSL-based applications affected by storage access problems

General Sentiment

Community reception is decidedly mixed. While users appreciate the fixes for RDS and audio issues, significant frustration persists over remaining unfixed problems. The emergency update is viewed as necessary but incomplete, with reports of AMD GPU driver timeouts, Explorer.exe crashes, and File History failures continuing unresolved. Users express concern about the spike in security fixes potentially introducing more instability, though there is acknowledgment that the security improvements are important. The update is generally seen as a step in the right direction but falling short of fully addressing the damage caused by the September 2026 Patch Tuesday release.

Known Issues

• Domain-joined devices with Credential Guard may lose secure channel with Active Directory domain after KB5124008 or later updates; users unable to sign in with valid domain credentials; workaround available through disabling Machine Identity Isolation
• USB Audio Class 1.0 devices may fail to start with error Code 10 or produce no audio output; volume controls unresponsive; Microsoft working on resolution
• Explorer.exe crashes reported in enterprise environments using Citrix UPM, FSLogix, Horizon, or ProfileUnity ProfileDisks
• File History unable to detect external backup drives on affected systems
• AMD Radeon GPU driver timeout errors and black screens reported on systems with RX 6600, RX 7700 XT, RX 7800 XT, RX 7900 GRE, RX 7900 XTX, and RX 9070 XT GPUs

Disclaimer: We take measures to ensure that AI-generated content is of the highest possible quality, but we cannot guarantee its accuracy and recommend that users do their own independent research. Generated on 2026-09-18 06:53 AM

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