Microsoft Support:
This cumulative update for Windows 11, version 26H1 (KB5127646) includes the latest security fixes and improvements, along with non-security updates from last month's optional preview release. Visit the Windows release health dashboard for the latest status on this release.
Improvements
This update includes new features and quality improvements that were part of the following update:- September 8, 2026—KB5124012 (OS Build 28000.2954)
- September 14, 2026—KB5129194 (OS Build 28000.2956) Out-of-band
- September 22, 2026—KB5124006 (OS Build 28000.3086)
- [Security updates] This update provides security improvements. For more information about the security vulnerabilities resolved by this update, see the Security Update Guide
- [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Certificate deployment via Windows updates continues across supported PCs and non-managed business devices in the coming months.
- [ReFS security] This update adds auditing and optional policy controls for ReFS volumes on externally attached storage devices. Auditing is enabled by default, while enforcement controls remain disabled by default to give administrators time to evaluate and prepare for future security hardening changes. To learn more, see KB5130741.
- [Windows Explorer (Known issue)] Fixed This update fixes an issue that affects Windows Explorer in multi-user environments, such as Azure Virtual Desktop and FSLogix. After sign-in, Explorer.exe might fail to start or repeatedly crash, causing a black screen.
- [Always On VPN] This update fixes an issue that affect Always On VPN connections after installing KB5124008. When automatic protocol selection or protocol fallback was configured, affected VPN connections could remain stuck in a Connecting state or fail to connect after an initial connection attempt failed. In some cases, subsequent connection attempts could display the error, "The specified port is already in use."
- [Storage Spaces Direct] This update fixes an issue that affects tiered Storage Spaces Direct virtual disks. Some virtual disks might fail to come online after installing certain security updates, making dependent clustered workloads unavailable.
- [Gaming] This update resolves an issue that could cause mouse input to stutter in some games.
Component updates
AI componentsThis release updates the following AI components to version 1.2608.951.0: Image Search, Content Extraction, Semantic Analysis, and Settings Model.
To learn more, see Release information for AI components.
Servicing stack update
Includes KB5127645 (Build 28000.3225), which improves the reliability of the Windows update installation process. To learn more about SSUs, see Simplifying on-premises deployment of servicing stack updates.
Known issues in this update
Symptoms
After installing the September 8, 2026, Windows security update (KB5124012), 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:
Resolution
This issue is partially resolved in the out-of-band (OOB) update released on September 14, 2026, (KB5129194). This OOB update resolves the symptoms experienced on devices using 8-channel or 3D audio modes. Microsoft is working to address the other symptoms and will provide more information when it is available.
IT administrators who need an immediate workaround for the symptoms not addressed yet by the OOB update should contact Microsoft Support for Business for assistance.
After installing the September 8, 2026, Windows security update (KB5124012), 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.
- Some devices might function in standard stereo configurations but fail when using multichannel audio features, including 8-channel or 3D audio modes. Some customers have reported that they're able to restore audio in these cases by switching to 2-channel mode.
Resolution
This issue is partially resolved in the out-of-band (OOB) update released on September 14, 2026, (KB5129194). This OOB update resolves the symptoms experienced on devices using 8-channel or 3D audio modes. Microsoft is working to address the other symptoms and will provide more information when it is available.
IT administrators who need an immediate workaround for the symptoms not addressed yet by the OOB update should contact Microsoft Support for Business for assistance.
How to get this update
Before you install this update
Microsoft 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.Deployment
If you deploy dynamic updates such as this update to an existing Windows image, ensure the boot.stl file is included as part of the installation media. Failure to include the file might prevent devices from successfully starting from the installation media and can result in error code 0xc0430001.Note: The boot.stl file is used during Secure Boot validation and must match the Windows version and architecture of the image you are updating.
To ensure the boot.stl file is included as part of the installation media, do one of the following:
- Use the Update WinPE script to update an existing Windows image. (Recommended)
- Manually copy the boot.stl file from the device Windows\Boot\EFI folder to the corresponding folder on your installation media before deploying the update.
Install this update
To install this update, use one of the following Windows and Microsoft release channels.Available | Next Step |
|---|---|
| This update downloads and installs automatically from Windows Update and Microsoft Update. |
|
| Before you install this update, the standalone package(s) for this update is available from the Microsoft Update Catalog website. This update contains MSU files that require installation in a specific order. You can install this update using Method 1 (install all MSU files together) or Method 2 (install each MSU file individually, in order) in the Arm64 installation instructions section. Note: This latest cumulative update includes updates for AI components. Even though the AI component updates are included in the update, the AI components are only applicable to Windows Copilot+ PCs and will not install on Windows PC or Windows Server. |
File information
For a list of the files provided in this update, download the file information for cumulative update KB5127646.For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5127646) - version 28000.3225.
Source:
October 13, 2026—KB5127646 (OS Build 28000.3231) | Microsoft Support
October 13, 2026—KB5127646 (OS Build 28000.3231)
support.microsoft.com
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