Windows 11 KB5129195 Emergency Update Fixes RDS, Plan9, and Some USB Audio Failures

Microsoft released KB5129195 on September 14, 2026, outside the normal Patch Tuesday schedule. The package targets Windows 11 version 24H2 and 25H2 and advances the operating systems to builds 26100.9457 and 26200.9457 respectively.

This is a cumulative security update, not a narrow hotfix. It includes the protections from the September 8 rollout, so a device can install KB5129195 directly even if administrators paused or removed the earlier package while troubleshooting.

Microsoft distributes the update through Windows Update, Windows Update for Business, WSUS and the Microsoft Update Catalog. Consumer devices using default Windows Update settings can receive it automatically, while managed fleets can stage deployment through their normal servicing rings.

The Remote Desktop regression was the most disruptive change. After the September update, RDS connections could drop after several minutes, sign-ins could fail and affected hosts could stop responding. Microsoft also documented hangs in tools such as MMC, the RDS Licensing Diagnoser, File Explorer and the Windows Update settings page.

KB5129195 contains Microsoft’s fix for that instability on Windows 11 24H2 and 25H2. Organizations that removed the September update to restore access can install this cumulative package to regain the security fixes and the RDS repair in one step.

The update also restores Plan9 host folder sharing for applications that create Linux virtual machines through the Host Compute System. Microsoft specifically names Windows Subsystem for Linux and Claude Cowork as affected scenarios. Conventional Hyper-V virtual machines that do not depend on Plan9 shares were outside the scope of this regression.

The September regression affects USB Audio Class 1.0 devices. Reported symptoms include a Code 10 error in Device Manager, no audio output, unresponsive volume controls and sound settings that fail to react.

KB5129195 fixes the failure on devices using 8-channel and 3D audio modes, but Microsoft does not describe the audio work as complete. Systems that still show Code 10, silent output or frozen controls remain under investigation, so administrators should test the exact hardware model rather than treating installation success as proof that audio is restored.

The package also adds protection for CVE-2026-62721, a Windows User-Mode Power Service elevation-of-privilege vulnerability. That security content gives organizations a reason to deploy the update even on systems that never encountered the RDS, Plan9 or audio regressions.

Microsoft lists a separate known issue for some domain-joined devices that use Credential Guard with Machine Identity Isolation enforcement. Affected systems can lose the secure trust relationship with their domain, creating authentication and management problems after the update.

The documented workaround is intended for administrators: temporarily disable the relevant enforcement, restore the machine’s secure channel, and follow Microsoft’s release-health guidance before re-enabling protections. Because that process changes a security control, it should be tested and approved through normal change management rather than applied broadly.

A sensible rollout starts with RDS session hosts and systems that depend on Plan9 shares, followed by a representative sample of USB audio hardware and domain-joined endpoints. Verify the new build, Remote Desktop connectivity, shared folders, audio output and the domain secure channel before expanding deployment.