October 20, 2025—KB5070773 (OS Build 26100.6901) Out-of-band
Applies To
Release Date:
10/20/2025
Version:
OS Build 26100.6901
Windows Secure Boot certificate expirationImportant: Secure Boot certificates used by most Windows devices are set to expire starting in June 2026. This might affect the ability of certain personal and business devices to boot securely if not updated in time. To avoid disruption, we recommend reviewing the guidance and taking action to update certificates in advance. For details and preparation steps, see Windows Secure Boot certificate expiration and CA updates.
To learn more about Windows update terminology, see types of Windows updates and the monthly quality update types. For an overview, see the update history page for Windows Server 2025.
Stay informed! Follow @WindowsUpdate for the latest updates from the Windows Release Health Dashboard.
Improvements
This out-of-band (OOB) update includes quality improvements. This update is cumulative and includes security fixes and improvements from the October 14, 2025, security update (KB5066835), in addition to the following:Â
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[USB] Fixed: After installing the Windows security update released on October 14, 2025 (KB5066835), USB devices, such as keyboards and mice, do not function in the Windows Recovery Environment (WinRE). This issue prevents navigation of any of the recovery options within WinRE. Note that the USB devices continue to work normally within the Windows operating system.
Windows Server 2025 servicing stack update (KB5067360)- 26100.6893
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
Active Directory domain controllers (DC) running on Windows Server 2025 and also running the schema master Flexible Single Master Operation (FSMO) role, will allow duplicate entries in attributes of schema objects. Commonly affected attributes include ​​​​​​​auxiliaryClass, possSuperiors, mayContain with values such as msExchBaseClass, msExchContainer,​​​​​​​ and msExchVirtualDirectoryFlags.​​​​​​​
When this occurs, Active Directory replication fails with a schema mismatch error, such as error 8418:Â The replication operation failed because of a schema mismatch between the servers involved."Â
This issue can be observed when running Exchange Server setup forestprep and the schema master role for Active Directory is running Windows Server 2025. This breaks replication in the entire Active Directory enterprise environment because the schema across domain controllers is now inconsistent.
Note:Â This issue appears to have existed since the initial release of Windows Server 2025, but recent Exchange Server cumulative updates (for Exchange Server SE) have exposed it.
Workaround
To work around the issue, manually remove the duplicate entries in the AD schema. If you would like help in generating a script to help remove the duplicate entries, contact Microsoft’s Support for business.
The issue is under investigation, and additional information will be shared as soon as it becomes available.
​​​​​​​Symptoms
After installing September 2025 security update (KB5065426), applications that use the Active Directory directory synchronization (DirSync) control for on-premises Active Directory Domain Services (AD DS), such as when using Microsoft Entra Connect Sync, can result in incomplete synchronization of large AD security groups exceeding 10,000 members.
Workaround
This issue can be mitigated using Known Issue Rollback (KIR) for enterprise-managed devices managed by IT departments that have installed the affected update and encountered this issue. IT administrators can resolve this issue by installing and configuring the special Group Policy listed below.Â
Group Policy downloads with Group Policy name:Â Â
Download for Windows 11, Versions 24H2 and 25H2 and Windows Server 2025 — Windows 11 24H2, Windows 11 25H2 and Windows Server 2025 KB5066835 251016_21401 Known Issue Rollback
The special Group Policy can be found in Computer Configuration > Administrative Templates > Windows 11 24H2, Windows 11 25H2 and Windows Server 2025 KB5066835 251016_21401 Known Issue Rollback. For information on deploying and configuring these special Group Policy, see How to use Group Policy to deploy a Known Issue Rollback.Â
Important: You will need to install and configure the Group Policy for Windows Server 2025. Then restart Windows Server 2025 to apply the group policy setting. (Windows 11 is out of scope of this notification and guidance.)
Alternatively, affected customers can apply the following registry key as a workaround to disable the feature change.
Warning: Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk. For more information, see Windows registry for advanced users.
​​​​​​​Path: Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Policies\Microsoft\FeatureManagement\Overrides
Name: 2362988687
Type: REG_DWORD
Value: 0
​​​​​​​The issue is under investigation, and additional information will be shared as soon as it becomes 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 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.
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Before you install this update To get the standalone package(s) for this update, go to the Microsoft Update Catalog website. This KB contains one or more MSU files that require installation in a specific order. Install this update Method 1: Install all MSU files together Download all MSU files for KB5070773 from Microsoft Update Catalog and place them in the same folder (for example, C:/Packages). Use Deployment Image Servicing and Management (DISM.exe) to install the target update. DISM will use the folder specified in PackagePath to discover and install one or more prerequisite MSU files as needed. Updating Windows PC To apply this update to a running Windows PC, run the following command from an elevated Command Prompt:
Or, run the following command from an elevated Windows PowerShell prompt:
Updating Windows Installation media To apply this update to Windows Installation media, see Update Windows installation media with Dynamic Update. To add this update to a mounted image, run the following command from an elevated Command Prompt:
Or, run the following command from an elevated Windows PowerShell prompt:
​​​​​​​​​​​​​​ Method 2: Install each MSU file individually, in order Download and install each MSU file individually either using DISM or Windows Update Standalone Installer in the following order:
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1 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.
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If you want to remove the LCU
To remove the LCU after installing the combined SSU and LCU package, use the DISM/Remove-Package command line option with the LCU package name as the argument. You can find the package name by using this command: DISM /online /get-packages.
Running Windows Update Standalone Installer (wusa.exe) with the /uninstall switch on the combined package will not work because the combined package contains the SSU. You cannot remove the SSU from the system after installation.
File information
For a list of the files in this update, download the file information for cumulative update 5070773.
For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5067630) - version 26100.6893.
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