September 8, 2026—KB5122878 (OS Builds 19045.7725 and 19044.7725)

Applies To
Windows 10 ESU Windows 10 Enterprise LTSC 2021 Windows 10 IoT Enterprise LTSC 2021

Important

Free support for Windows 10 Enterprise LTSC 2021 will end soon. For information about the availability of an Extended Security Update (ESU), see the End of support section.

Summary

This article lists the security issues and quality improvements included in this cumulative security update.

Applies to: Windows 10 ESU

Important

Use EKB KB5015684 to update to Windows 10, version 22H2.

This security update includes fixes and quality improvements that are part of the following updates:

The following is a summary of the issues that this update addresses when you install this update. If there are new features, it lists them as well. The bold text within the brackets indicates the item or area of the change we are documenting.

  • [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.

  • [OMA DM protocol] This update improves the logging features of the OMA DM Client (omadmclient.exe) component. More debug information is now saved when connecting to a server.

  • [Windows Code Integrity policies] Improves application compatibility during Windows certificate-authority rotation by recognizing Microsoft Windows Production PCA 2026 RSA2048-SHA256 as equivalent to PCA 2011.

  • [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.

  • [BitLocker Group Policy] This update addresses the "Devices with an unrecommended BitLocker Group Policy configuration might be required to enter their BitLocker recovery key" known issue.

If you installed earlier updates, only the new updates contained in this package will be downloaded and installed on your device.

For more information about security vulnerabilities, please refer to the new Security Update Guide website and the September 2026 Security Updates.

For information about Windows update terminology, see the article about the types of Windows updates and the monthly quality update types. For an overview of Windows 10, version 22H2, see its update history page.

Known issues in this update

Remote Desktop Services might stop responding after September 2026 security update

Symptoms

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.

Note

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

Resolution

This issue is resolved in Windows updates released on and after September 14, 2026 such as KB5129236. We recommend you install the latest Windows update for your device as it contains important improvements and issue resolutions, including this one.

File History might stop working after installing September 2026 Windows update

Symptoms

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 previous version available." In some cases, Event Viewer might record application crash events referencing FileHistory.exe and KERNELBASE.dll.

Resolution

Microsoft is working on a resolution for this issue in a future Windows update and will provide more information when it is available.

Available Next Step
Available This update will be downloaded and installed automatically from Windows Update.

File information

A list of the files that are included in this update are provided in a CSV (Comma delimited) (*.csv) file. The file can be opened in a text editor such as Notepad or in Microsoft Excel.

Note The English (United States) version of this software update might contain files for additional languages.

Download Download the file information for cumulative update KB5122878.

Download Download the file information for update SSU (KB5122877) - version 19041.7714.

Change log

Change date Description
September 19, 2026 Added a known issue, "File History might stop working after installing September 2026 Windows update".
September 14, 2026 Added the resolution for the known issue "Remote Desktop Services might stop responding after September 2026 security update".
September 12, 2026 Added a known issue, "Remote Desktop Services might stop responding after September 2026 security update".
September 8, 2026 Known issue updated: "Devices with an unrecommended BitLocker Group Policy configuration might be required to enter their BitLocker recovery key". For more information, see a Windows update released on or after April 14, 2026 such as KB5082200.