This out-of-band update for Windows 11, version 23H2 (KB5129242) is cumulative. It includes updates from previous security releases, along with additional improvements. Visit the Windows release health dashboard for the latest status on this release.
Announcements and messages
This section provides key notifications related to this release, including announcements, change logs, and end-of-support notices.
Windows Secure Boot certificate expiration
Windows Secure Boot certificate expiration
Important
Secure Boot certificates used by most Windows devices started to expire on June 2026. Microsoft has been updating these certificates on PCs and non-managed business devices for the past months. Devices that haven't received the newer certificates will continue to start, and standard Windows updates will continue to install. We will continue to install the newer certificates via Windows updates in the coming months.
Improvements
This OOB update includes quality improvements. This update is cumulative and includes security fixes and improvements from the September 8, 2026, security update (KB5122880), in addition to the following:
[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.)
Windows 11 servicing stack update (KB5122879) - 22621.7578
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
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 and Servicing Stack Updates (SSU): Frequently Asked Questions.
Install this update
To install this update, use one of the following Windows and Microsoft release channels.
| Available | Next Step |
|---|---|
|
Open Start 
> Settings 
> Windows Update > Advanced options > Optional updates. In the Optional updates available area, you will find the link to download and install available updates.Check for optional updates |
File Information
For a list of the files provided in this update, download the file information for cumulative update 5129242.
For a list of the files provided in the servicing stack update, download the file information for SSU KB5122879 - versions 22621.7578.