October 23, 2025—KB5070881 (OS Build 26100.6905) Out-of-band
Applies To
Release Date:
10/23/2025
Version:
OS Build 26100.6905
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 update and 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:
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[Windows Server Update Services (WSUS)] Fixed: This update addresses a remote code execution (RCE) vulnerability that was identified in WSUS reporting web services. For more information about the security fix, see CVE-2025-59287.
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: The replication operation failed because of a schema mismatch between the servers involved."
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: 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.
Group Policy downloads with Group Policy name:
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.
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.
After installing this update or later updates, Windows Server Update Services (WSUS) does not display synchronization error details within its error reporting. This functionality is temporarily removed to address the Remote Code Execution Vulnerability, CVE-2025-59287.
Symptoms
After installing the security October update (KB5066835) for Windows Server 2025, server-side applications that rely on HTTP.sys might experience issues with incoming connections. As a result, Internet Information Services (IIS) websites might fail to load and display an error message such as “Connection reset – error (ERR_CONNECTION_RESET)” or a similar message. This includes websites hosted on http://localhost/ and other IIS connections.
This issue may result from various conditions, including internet connectivity, timing of update installation, and device restarts. It might not occur in all environments, even if the update is installed.
The following steps can help resolve this issue in environments where it's observed:
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On the affected device, open Settings and go to Windows Update.
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Select Start , type Check for updates, and Check for updates from the results.
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If updates are available, install them.
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Restart your device.
Note: Make sure to restart your device, even if no updates are installed.
Workaround
IT administrators can resolve this issue by installing and configuring the special Group Policy listed below.
Group Policy downloads with Group Policy name:
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Download for Windows 11, version 24H2, Windows 11 25H2 and Windows Server, version 2025—Windows 11 24H2, Windows 11 25H2 and Windows Server 2025 KB5066835 251015_22001 Known Issue Rollback.msi
For information on deploying and configuring these special Group Policy, see How to use Group Policy to deploy a 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 251015_22001 Known Issue Rollback.
The issue is under investigation, and additional information will be shared as soon as it becomes available.
Symptoms
This update was briefly offered to all Windows Server 2025 machines, regardless of their Hotpatch enrollment status. A very limited number of Hotpatch-enrolled machines received the update before the issue was corrected. The update is now offered only to machines that are not enrolled to receive Hotpatch updates.
This issue only impacts Windows Server 2025 devices and virtual machines (VMs) enrolled to receive Hotpatch updates.
Workaround
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For machines that downloaded and installed this update: Machines that installed this update are temporarily "off the Hotpatch train" and will not be offered Hotpatch updates in November and December. They will instead be offered the regular monthly security updates that require a restart of the device. After they install the planned baseline in January 2026, they will again be offered Hotpatch updates. The next planned Hotpatch update would be offered in February 2026.
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For machines that downloaded, but have not yet installed, this update: Go to Settings > Windows Update and select Pause updates. Then un-pause and scan for updates. You will then be offered the correct update.
How do Hotpatch machines get the fix contained in this update?
Hotpatch-enrolled machines that have not installed this update will be offered the October 24, 2025, Security Update for Windows Server Update Services (KB5070893) on top of the planned baseline update for October 2025 (KB5066835). Machines installing KB5070893 will remain "on the Hotpatch train" and will continue to receive Hotpatch updates in November and December. Only those machines that have WSUS enabled will be prompted to restart after installing the Security Update, KB5070893.
If you have any questions, please contact Microsoft Support for business.
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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This update downloads and installs automatically from Windows Update and Microsoft Update. |
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This update downloads and installs automatically from Windows Update for Business in accordance with configured policies. |
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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 KB5070881 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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his update will automatically sync with Windows Server Update Services (WSUS) if you configure Products and Classifications as follows: Product: Microsoft Server operating system-24H2 Classification: Security Updates |
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 5070881.
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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