UPDATE 9/22:
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This out-of-band update for Windows 11, version 26H1 (KB5129194) includes the latest fixes and improvements. Visit the Windows release health dashboard for the latest status on this release.
Change log
This 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 updateIncludes KB5125104 (Build 28000.2950), which improves the reliability of the Windows update installation process.
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:
For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5125104) - version 28000.2950.
support.microsoft.com
Check Windows Updates
UUP Dump:
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ARM64 ISO download:
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KB5124006 Windows 11 Cumulative Update Preview build 28000.3086 (26H1) - Sept. 22
UPDATE 10/13: https://www.elevenforum.com/t/kb5127646-windows-11-cumulative-update-build-28000-3231-26h1-oct-13.50116/ Microsoft Support: This cumulative update for Windows 11, version 26H1 (KB5124006), includes production-quality improvements. Announcements and messages This section provides...
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Microsoft Support:
This out-of-band update for Windows 11, version 26H1 (KB5129194) includes the latest fixes and 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 out-of-band update includes the following improvements:- [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 (KB5124012). 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
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 updateIncludes KB5125104 (Build 28000.2950), which improves the reliability of the Windows update installation process.
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.
Workaround
Affected customers can apply one of the following workarounds to mitigate the issue:
Group Policy downloads with Group Policy name:
You will need to install and configure the Group Policy for your version of Windows to resolve this issue. You will also need to restart your device(s) to apply the group policy setting. Note that this Group Policy will disable the change causing this issue until a resolution is released in a future Windows update.
For information on deploying and configuring this special Group Policy, please see How to use Group Policy to deploy a Known Issue Rollback
Resolution
We are working on a resolution for this issue, and it will be released in a future Windows update.
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.
Workaround
Affected customers can apply one of the following workarounds to mitigate the issue:
- Manually launch explorer.exe: Users can temporarily mitigate this issue by opening Task Manager (Ctrl+Shift+Esc), selecting Run new task, entering explorer.exe, and selecting OK.
- Mitigate through Known Issue Rollback (KIR): This issue is mitigated using Known Issue Rollback (KIR).
Group Policy downloads with Group Policy name:
- Download for Windows 11, version 25H2 and Windows 11, version 24H2: KB5124010 260924_20021 Known Issue Rollback
You will need to install and configure the Group Policy for your version of Windows to resolve this issue. You will also need to restart your device(s) to apply the group policy setting. Note that this Group Policy will disable the change causing this issue until a resolution is released in a future Windows update.
For information on deploying and configuring this special Group Policy, please see How to use Group Policy to deploy a Known Issue Rollback
Resolution
We are working on a resolution for this issue, and it will be released in a future Windows update.
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.
To work around this issue, disable Machine Identity Isolation using the same management method that was used to enable it. Choose the applicable option below:
Then reset the secure channel using the following command:
Resolution
Microsoft plans to resolve this issue in a future Windows update by temporarily preventing Machine Identity Isolation enforcement while improvements are made to the feature.
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.
Workaround
Important: This section contains information about modifying the registry. Before you modify the registry, back it up and make sure that you know how to restore it if a problem occurs. For more information, see How to back up and restore the registry in Windows.To work around this issue, disable Machine Identity Isolation using the same management method that was used to enable it. Choose the applicable option below:
- If Machine Identity Isolation was enabled by Intune policy, disable Machine Identity Isolation with Intune.
- If Machine Identity Isolation was enabled by Group Policy, disable Machine Identity Isolation with Group Policy.
- If Machine Identity Isolation was enabled directly in the registry, use these steps to disable it:
- On the Windows 11, version 24H2 or 25H2 device, locate the following registry paths:
HKLM\SYSTEM\CurrentControlSet\Control\Lsa\MachineIdentityIsolation
HKLM\SOFTWARE\Policies\Microsoft\Windows\DeviceGuard\MachineIdentityIsolation - For either of these registry keys, if the value of MachineIdentityIsolation is set to 2, change it to:
MachineIdentityIsolation = 0
- On the Windows 11, version 24H2 or 25H2 device, locate the following registry paths:
Then reset the secure channel using the following command:
Test-ComputerSecureChannel -Repair -Credential (Get-Credential)Resolution
Microsoft plans to resolve this issue in a future Windows update by temporarily preventing Machine Identity Isolation enforcement while improvements are made to the feature.
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 KB5124006. 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 KB5124006. 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 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 out-of-band 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. |
File information
For a list of the files provided in this update, download the file information for out-of-band update KB5129194.For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5125104) - version 28000.2950.
Source:
September 14, 2026—KB5129194 (OS Build 28000.2956) Out-of-band | Microsoft Support
September 14, 2026—KB5129194 (OS Build 28000.2956) Out-of-band
support.microsoft.com
Check Windows Updates
UUP Dump:
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ARM64 ISO download:
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Select language for Windows 11, version 26H1 (28000.2956) arm64 on UUP dump. UUP dump lets you download Unified Update Platform files, like Windows Insider updates, directly from Windows Update.
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UUP Dump - Download Windows Insider ISO
UUP Dump is the most practical and easy way to get ISO images of any Insider Windows 10 or Windows 11 version, as soon as Microsoft has released a new build. UUP Dump creates a download configuration file according to your choices, downloads necessary files directly from Microsoft servers, and...
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