UPDATE 9/22:
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This out-of-band (OOB) update for Windows 11, version 25H2 and Windows 11, version 24H2 (KB5129195) is cumulative. It includes updates from previous releases, along with additional security and non-security improvements. Visit the Windows release health dashboard for the latest status on this release.
Change log
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.
File Information
For a list of the files provided in this update, download the file information for cumulative update KB5129195.
For a list of the files provided in the servicing stack update, download the file information for SSU KB5124007 - versions 22621.9441.
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KB5124010 Windows 11 Cumulative Update Preview build 26100.9550 (24H2), 26200.9550 (25H2), and 26300.9550 (26H2) - Sept. 22
UPDATE 10/13: https://www.elevenforum.com/t/kb5127648-windows-11-cumulative-update-build-26100-9711-24h2-26200-9711-25h2-26300-9711-26h2-oct-13.50115/ Microsoft Support: This cumulative update for Windows 11, versions 26H2, 25H2, and 24H2 (KB5124010), includes production-quality improvements...
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Microsoft Support:
This out-of-band (OOB) update for Windows 11, version 25H2 and Windows 11, version 24H2 (KB5129195) is cumulative. It includes updates from previous releases, along with additional security and non-security improvements. Visit the Windows release health dashboard for the latest status on this release.
Change log
Change date | Change description |
|---|---|
| September 18, 2026 | Added a known issue, "Domain-joined devices might lose their secure trust relationship with the domain". |
Improvements
This OOB update includes the following improvement:- [Security] This update includes protections documented in CVE-2026-62721, which refers to a Windows User-Mode Power Service (UMPS) Elevation of Privilege vulnerability.
- [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.)
Component updates
Windows 11 servicing stack update (KB5124007) - 22621.9441
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
Symptoms
After installing the August 2026 Windows non-security preview update KB5120998 and subsequent updates, some devices might experience desktop loading issues. This issue has been primarily observed on Azure Virtual Desktop (AVD) hosts using FSLogix. This issue appears to occur more frequently with some existing user profiles.
Affected users might see a black screen after sign-in, with the desktop session failing to load automatically. In some cases, users might be unable to access their desktop until the desktop session is started manually. Application event logs might also show Windows Explorer crashes.
Resolution
This issue is resolved in Windows updates released on and after October 13, 2026 such as KB5127648. 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 August 2026 Windows non-security preview update KB5120998 and subsequent updates, some devices might experience desktop loading issues. This issue has been primarily observed on Azure Virtual Desktop (AVD) hosts using FSLogix. This issue appears to occur more frequently with some existing user profiles.
Affected users might see a black screen after sign-in, with the desktop session failing to load automatically. In some cases, users might be unable to access their desktop until the desktop session is started manually. Application event logs might also show Windows Explorer crashes.
Resolution
This issue is resolved in Windows updates released on and after October 13, 2026 such as KB5127648. We recommend you install the latest Windows update for your device as it contains important improvements and issue resolutions, including this one.
Symptoms
After installing the September 8, 2026, Windows security update (KB5124008), or later updates, some Credential Guard protected machine accounts might lose their secure channel with an on-premises Active Directory (AD) domain. Users might then be unable to sign in interactively with valid domain credentials and might receive a message stating that the trust relationship between the device and the domain failed. Offline sign-in using previously cached credentials might continue to work. AD replication and AD services on the domain controllers are not affected.
This issue occurs because KB5124008 and later updates enable the Machine Identity Isolation feature. While the update does not directly enable Machine Identity Isolation enforcement, it does cause Windows to begin honoring any existing or policy-provisioned settings that enabled Machine Identity Isolation enforcement. However, this feature is only supported for environments connected to domain controllers running at a Windows Server 2025 Domain Functional Level (DFL) and above. The feature should be disabled elsewhere. Any devices previously configured to use Machine Identity Isolation that are not connected to Windows Server 2025 domain controllers will experience this issue and will need to disable the feature.
Resolution
This issue is addressed by KB5124010. This update prevents Machine Identity Isolation (MII) enforcement by disabling it completely while improvements are made to the feature. MII enforcement will be prevented regardless of the MII configuration.
After installing the September 8, 2026, Windows security update (KB5124008), or later updates, some Credential Guard protected machine accounts might lose their secure channel with an on-premises Active Directory (AD) domain. Users might then be unable to sign in interactively with valid domain credentials and might receive a message stating that the trust relationship between the device and the domain failed. Offline sign-in using previously cached credentials might continue to work. AD replication and AD services on the domain controllers are not affected.
This issue occurs because KB5124008 and later updates enable the Machine Identity Isolation feature. While the update does not directly enable Machine Identity Isolation enforcement, it does cause Windows to begin honoring any existing or policy-provisioned settings that enabled Machine Identity Isolation enforcement. However, this feature is only supported for environments connected to domain controllers running at a Windows Server 2025 Domain Functional Level (DFL) and above. The feature should be disabled elsewhere. Any devices previously configured to use Machine Identity Isolation that are not connected to Windows Server 2025 domain controllers will experience this issue and will need to disable the feature.
Resolution
This issue is addressed by KB5124010. This update prevents Machine Identity Isolation (MII) enforcement by disabling it completely while improvements are made to the feature. MII enforcement will be prevented regardless of the MII configuration.
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:
Resolution
Microsoft is working on a resolution and will update this documentation when more information is available.
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.
Resolution
Microsoft is working on a resolution and will update this documentation when more information is available.
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
This issue is resolved in Windows updates released on and after September 22, 2026 such as KB5124010. 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 previous version available." In some cases, Event Viewer might record application crash events referencing FileHistory.exe and KERNELBASE.dll.
Resolution
This issue is resolved in Windows updates released on and after September 22, 2026 such as KB5124010. We recommend you install the latest Windows update for your device as it contains important improvements and issue resolutions, including this one.
How to get this update
Before you install this updateMicrosoft 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 |
|---|---|
| This update downloads and installs automatically from Windows Update and Microsoft Update. |
|
| 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. |
File Information
For a list of the files provided in this update, download the file information for cumulative update KB5129195.
For a list of the files provided in the servicing stack update, download the file information for SSU KB5124007 - versions 22621.9441.
Source:
September 14, 2026—KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band | Microsoft Support
September 14, 2026—KB5129195 (OS Builds 26200.9457 and 26100.9457) Out-of-band
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