5122880

This cumulative update for Windows 11, version 23H2 (KB5122880), 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.

Announcements and messages

This section provides key notifications related to this release, including announcements, change logs, and end-of-support notices.

Important: Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. Microsoft has been updating these certificates on consumer and non-managed business devices over the past several months. Devices that haven’t received the newer certificates will continue to start and operate normally, and standard Windows updates will continue to install. Updated certificates will continue to be delivered through Windows Update in the coming months.

Windows 11. Version 23H2 Enterprise and Education will reach end of updates on November 10, 2026. Devices running these editions will no longer receive fixes for known issues, time zone updates, technical support, or monthly security and preview updates containing protections from the latest security threats.

To stay protected and up to date, we recommend you upgrade to the latest version of Windows 11 .

This update addresses security issues for your Windows operating system.

Use EKB KB5027397 to update to Windows 11, version 23H2.

This security update contains fixes and quality improvements from KB5120240 (released August 11, 2026). The following summary outlines key issues addressed by this update. Also, included are available new features. The bold text within the brackets indicates the item or area of the change.

[Security updates] This update provides security improvements. For more information 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.

[Date and Time] This update adjusts Morocco Standard Time to reflect Morocco's transition to permanent UTC+00:00 effective September 20, 2026. This change ensures that the correct local time is displayed after the transition.

[Cellular] Updating COSA profiles for Telavox and Swisscom.

[OMA DM] This update improves the logging features of the Omadmclient component. More debug information is now saved when connecting to a server.

[Remote Desktop] This update addresses an issue that affects Remote Desktop audio redirection. Audio from the remote session might not play on the local computer in certain configurations.

If you've already installed updates, your device will download and install only the new updates included in this package.

Windows 11 servicing stack update (KB5122879) - 22621.7578

Known issues in this update

After installing the September 2026 security update KB5122880 , applications that use HCS-managed virtual machines might experience issues when sharing host folder with Linux VMs using Plan9. Affected virtual machines start normally, but folders shared from the Windows host using Plan9 do not appear or cannot be accessed in the guest environment.

Applications or sandbox environments that depend on these shared folders might display an error indicating that no Plan9 drive shares were mounted. Claude Cowork and the Windows Subsystem for Linux (WSL) are two of the applications affected by this issue. Standard Hyper-V virtual machines that do not use the Plan9 feature are not affected by this issue.

Microsoft is working on a resolution and will update this documentation when more information is available.

After installing the September 2026 Windows security update, some organizations might experience issues with Remote Desktop Services (RDS).

In some environments, RDS might become unstable, resulting in RDP connections failing after several minutes, sign-in issues, or servers hanging at "Please wait for the Remote Desktop Configuration". Related tools, including Microsoft Management Console (MMC), RDS Licensing Diagnoser, and File Explorer might also become unresponsive. Additionally, the Windows Update page might stop responding and continuously display a loading indicator.

This issue does not affect Windows 365 or Azure Virtual Desktop.

This issue is resolved in Windows updates released on and after September 14, 2026 such as KB5129242 . We recommend you install the latest Windows update for your device as it contains important improvements and issue resolutions, including this one.

After installing the September 2026 Windows security update KB5124008 , some customers using File History, might be unable to create or update backups. File History, available through Control Panel > System and Security > File History , is used to back up files to an external drive or network location. Affected devices might incorrectly display a "Reconnect your drive" message even when a compatible backup drive is connected and functioning properly. Additionally, the "Last Backup" timestamp might not update, and previously backed up files might show "No version available." In some cases, Event Viewer might record application crash events referencing FileHistory.exe and KERNELBASE.dll .

Microsoft is working on a resolution for this issue in a future Windows update and will provide more information when it 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 latest cumulative update (LCU). For general information SSUs, see Servicing stack updates .

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 .

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.

For information how to apply Dynamic Update packages to existing Windows images, see Update Windows installation media with Dynamic Update .

To install this update, use one of the following Windows and Microsoft release channels.

Server Update Services

Classification : Security Updates

For a list of the files provided in this update, download the file information for cumulative update KB5122880 .

For a list of the files provided in the servicing stack update, download the file information for SSU KB5122879 - versions 22621.7578 .

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