This out-of-band (OOB) update for Windows Server 2025 (KB5129235) is a non-security cumulative update.
Improvements
This out-of-band update contains quality improvements from KB5122871 (released September 8, 2026). The following summary outlines key issues addressed by this out-of-band update. The bold text within the brackets indicates the item or area of the change.
[Remote Desktop Services (known issue)] Fixed: This update addresses an issue affecting Remote Desktop Services (RDS) after installing the September 2026 Windows security update (KB5122871). 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.
[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.)
If you installed earlier updates, your device downloads and installs only the new updates contained in this package.
Windows Server 2025 servicing stack update (KB5122870) - 26100.33434
This update makes quality improvements to the servicing stack, which is the component that installs Windows updates. Servicing stack updates (SSU) ensure that you have a robust and reliable servicing stack so that your devices can receive and install Microsoft updates. To learn more about SSUs, see Simplifying on-premises deployment of servicing stack updates.
Known issues in this update
Windows Server Update Services (WSUS) does not display error details
After installing KB5070881 or later updates, Windows Server Update Services (WSUS) does not display synchronization error details within its error reporting. This functionality is temporarily removed to address the Remote Code Execution Vulnerability, CVE-2025-59287.
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 now combines the latest servicing stack update (SSU) for your operating system with the latest cumulative update (LCU). For general information about SSUs, see Servicing stack updates.
Install this update
To install this update, use one of the following Windows and Microsoft release channels.
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To install this update, download the standalone package(s) for this update from the Microsoft Update Catalog. This update contains MSU files that require installation in a specific order. Follow the Arm64 installation instructions or x64 installation instructions, as appropriate.
If you install additional Dynamic Update packages, use versions from the same release month as this update. If a Safe OS Dynamic Update or Setup Dynamic Update is not available for the same release month, use the most recently released version.
Note This latest cumulative update includes updates for AI components. AI components are applicable only to Copilot+ PCs and will not install on other Windows client PCs or Windows Server. |
Arm64 installation instructions
Note The Microsoft Update Catalog may include one or more required checkpoint cumulative updates and the target cumulative update. Install the checkpoint cumulative updates in order before installing the target cumulative update.
Download all MSU files for update KB5129235 from the Microsoft Update Catalog and place them in the same folder (for example, C:/Packages). Ensure no other files are present in the folder.
This update consists of the following update file(s).
| Item |
MSU file |
| Required checkpoint cumulative update |
windows11.0-kb5043080-arm64.msu |
| Target cumulative update |
windows11.0-kb5129235-arm64.msu |
Method 1: Install each MSU file individually, in order
Double-click each file in the following order to install that update (if there is more than one .msu file listed):
- windows11.0-kb5043080-arm64.msu
- windows11.0-kb5129235-arm64.msu
Note If a required checkpoint cumulative update is already present, a message will indicate that the update is already installed. For guidance on using the Windows Update Standalone Installer (Wusa.exe), see Description of the Windows Update Standalone Installer in Windows.
Method 2: Install all MSU files together
Use Deployment Image Servicing and Management (DISM.exe) to install the target cumulative update. DISM automatically scans the folder specified in the PackagePath folder and installs any required checkpoint cumulative updates.
Updating a Windows PC
To apply this update on a running Windows PC, run the following command from an elevated Command Prompt window:
DISM /Online /Add-Package /PackagePath:c:\packages\windows11.0-kb5129235-arm64.msu
Or, run the following command from an elevated PowerShell window:
`Add-WindowsPackage -Online -PackagePath "c:\packages\windows11.0-kb5129235-arm64.msu"'
Updating Windows installation media
To apply this update to Windows installation media, see Update Windows installation media with Dynamic Update.
To add this update to a mounted image, run the following command from an elevated Command Prompt window:
DISM /Image:mountdir /Add-Package /PackagePath:windows11.0-kb5129235-arm64.msu
Or, run the following command from an elevated PowerShell window:
Add-WindowsPackage -Path "c:\\offline" -PackagePath "windows11.0-kb5129235-arm64.msu" -PreventPending
x64 installation instructions
Note The Microsoft Update Catalog may include one or more required checkpoint cumulative updates and the target cumulative update. Install the checkpoint cumulative updates in order before installing the target cumulative update.
Download all MSU files for update KB5129235 from the Microsoft Update Catalog and place them in the same folder (for example, C:/Packages). Ensure no other files are present in the folder.
This update consists of the following update file(s).
| Item |
MSU file |
| Required checkpoint cumulative update |
windows11.0-kb5043080-x64.msu |
| Target cumulative update |
windows11.0-kb5129235-x64.msu |
Method 1: Install each MSU file individually, in order
Double-click each file in the following order to install that update (if there is more than one .msu file listed):
- windows11.0-kb5043080-x64.msu
- windows11.0-kb5129235-x64.msu
Note If a required checkpoint cumulative update is already present, a message will indicate that the update is already installed. For guidance on using the Windows Update Standalone Installer (Wusa.exe), see Description of the Windows Update Standalone Installer in Windows.
Method 2: Install all MSU files together
Use Deployment Image Servicing and Management (DISM.exe) to install the target cumulative update. DISM automatically scans the folder specified in the PackagePath folder and installs any required checkpoint cumulative updates.
Updating a Windows PC
To apply this update on a running Windows PC, run the following command from an elevated Command Prompt window:
DISM /Online /Add-Package /PackagePath:c:\packages\windows11.0-kb5129235-x64.msu
Or, run the following command from an elevated PowerShell window:
`Add-WindowsPackage -Online -PackagePath "c:\packages\windows11.0-kb5129235-x64.msu"'
Updating Windows installation media
To apply this update to Windows installation media, see Update Windows installation media with Dynamic Update.
To add this update to a mounted image, run the following command from an elevated Command Prompt window:
DISM /Image:mountdir /Add-Package /PackagePath:windows11.0-kb5129235-x64.msu
Or, run the following command from an elevated PowerShell window:
Add-WindowsPackage -Path "c:\\offline" -PackagePath "windows11.0-kb5129235-x64.msu" -PreventPending
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File Information
For a list of the files provided in this update, download the file information for cumulative update KB5129235.
For a list of the files provided in the servicing stack update, download the file information for SSU KB5122870 - version 26100.33434.
