New Update Microsoft KB5129195 Out-of-band

[czesetfan]

Microsoft released KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band:

Improvements
This OOB update includes the following improvement:

[Security] This update includes protections documented in CVE-2026-62721, which refers to a Windows User-Mode Power Service (UMPS) Elevation of Privilege vulnerability.

[Remote Desktop Services (known issue)] Fixed: This update addresses an issue affecting Remote Desktop Services (RDS) after installing the September 2026 Windows security update (KB5122880). In affected environments, RDS might become unstable, causing RDP connection and sign-in failures or servers to become unresponsive during Remote Desktop configuration. Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, File Explorer, and the Windows Update page, might also stop responding.

[Hyper-V (known issue)] Fixed: Some applications that use HCS-managed virtual machines experienced issues when sharing host folder with Linux VMs using Plan9. Folders shared from the Windows host using Plan9 did not appear or could not be accessed in the guest environment.

[8-channel or 3D audio modes] Fixed: Some USB Audio Class 1.0 devices functioning as expected in standard stereo configurations failed when using multichannel audio features, including 8-channel or 3D audio modes. (Note: There are other audio symptoms not resolved in this OOB update. See the “Known issues in this update” section for more information.)

September 14, 2026—KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band | Microsoft Support

 

[Bot AI]

Microsoft released KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band:

September 14, 2026—KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band | Microsoft Support

Hi, useful heads-up: KB5129195 is a cumulative out-of-band update for Windows 11 24H2 and 25H2, and it is worth installing promptly because it adds protection for CVE-2026-62721 as well as fixing several regressions from the September update.

What it fixes​

Area	Practical effect
Security	Adds protection for a Windows User-Mode Power Service elevation-of-privilege vulnerability
Remote Desktop Services	Fixes instability, failed RDP connections/sign-ins and associated interface hangs after KB5122880
Hyper-V / Plan9	Restores access to Windows host folders shared with HCS-managed Linux VMs
USB multichannel audio	Fixes failures involving 8-channel and 3D modes on some USB Audio Class 1.0 devices

The update applies to Windows 11 24H2 and 25H2, all editions, producing builds 26100.9457 and 26200.9457 respectively. It is cumulative, so previous fixes are included rather than requiring a chain of separate installations. [1]

Important audio limitation​

This is not a complete fix for the September USB-audio problems. Microsoft still lists a known issue affecting some USB Audio Class 1.0 devices, with symptoms including:

• Device Manager Code 10
• no audio output
• volume stuck at zero or unresponsive
• unavailable or unresponsive sound settings

Microsoft says it is still working on that remaining issue. Therefore, installing KB5129195 may restore multichannel modes yet leave a device with these broader symptoms unfixed. Similar subject matter, different bug—Windows audio apparently wanted an encore. [1]

Recommended next steps​

1. Install it through Windows Update; Microsoft states that it downloads and installs automatically. Managed environments can use their normal business deployment channel.
2. Restart if Windows requests it, then confirm the OS build with `winver`: 26100.9457 for 24H2 or 26200.9457 for 25H2.
3. On RDS hosts, verify a new RDP sign-in and open the management tools that were hanging.
4. If using HCS/Plan9 sharing, confirm the host folder appears and is accessible inside the Linux guest.
5. If USB audio remains broken with Code 10, no output or frozen controls, do not assume the update failed to install—the unresolved known issue may still apply. Check the Windows release-health entry for Microsoft's later resolution rather than repeatedly reinstalling this package.

[1]

Sources

1. September 14, 2026—KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band | Microsoft Support

 

[Zero Knowledge]

Power service exploit oh my this is like the print spooler RCE