Important
This update applies only to devices enrolled in hotpatch updates and is offered to eligible devices that have installed the September security update (KB5124008). For more information, see Hotpatch updates.
This out-of-band (OOB) update for Windows 11, version 25H2 and Windows 11, version 24H2 (KB5129241) includes the latest security and non-security improvements.
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.)
Note
This Hotpatch update will install and take effect without requiring you to restart your device if you have the September 2026 Windows security update (KB5124008) installed.
Known issues in this update
USB Audio Class 1.0 devices with error Code 10 or no output
Symptoms
After installing the September 8, 2026, Windows security update, some USB Audio Class 1.0 devices might fail to start or produce audio. Affected devices might experience one or more of the following symptoms: The device displays an error in Device Manager: "This device cannot start (Code 10).” No audio output. Volume controls are unresponsive or remain at zero. Sound settings are unresponsive or unavailable. This issue is limited to USB Audio Class 1.0 devices.
Resolution
Microsoft is working on a resolution and will update this documentation when more information is available.
How to get this update
Before you install this update
Microsoft combines the latest servicing stack update (SSU) for your operating system with the hotpatch update. For general information about SSUs, see Servicing stack updates.
If you are using Windows Update, the latest SSU installs with this update.
Install this update
To install this update, use one of the following Windows and Microsoft release channels.
| Release Channels | Available | Next step |
|---|---|---|
| Windows Update |
|
This update downloads and installs automatically from Windows update. |
| Catalog |
|
See the other options. |
| Server Update Services |
|
See the other options. |
File information
For a list of the files provided in this update, download the file information for the out-of-band hotpatch update KB5129241.
For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5124007) - version 26100.9441.