October 14, 2025—KB5066780 (OS Build 25398.1913)
Applies To
Release Date:
10/14/2025
Version:
OS Build 25398.1913
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 monthly quality update types. For an overview, see the update history page for Windows Server, version 23H2.
ImprovementsÂ
This security update contains fixes and quality improvements from KB5065425 (released September 9, 2025). The following summary outlines key issues addressed by this update. Also, included are available new features. The bold text within the brackets indicates the item or area of the change.
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[Input]
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Fixed: An issue where some characters didn’t display correctly when using the Chinese Input Method Editor (IME).
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Fixed: This update addresses an issue where certain Chinese characters appeared as empty boxes in some text fields, such as those used in Connection Manager Administration Kit, when a character limit was set.​​​​​​​
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[Networking (known issue)] Fixed: This update addresses an issue where you might not be able to connect to shared files and folders if you're using the Server Message Block (SMB) v1 protocol on NetBIOS over TCP/IP NetBIOS (NetBT). This can happen after installing update KB5065425.
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[PowerShell] Fixed: This update addresses that affects PowerShell Remoting and Windows Remote Management (WinRM). Commands might time out after 10 minutes. ​​​​​​​
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[Stability issue]Â This update addresses an issue observed in rare cases after installing the May 2025 security update and subsequent updates causing devices to experience stability issues. Some devices became unresponsive and stopped responding in specific scenarios.
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[Compatibility]Â This update removes the ltmdm64.sys driver. Fax modem hardware dependent on this specific driver will no longer work in Windows.
If you've already installed previous updates, your device will download and install only the new updates included in this package.
For more information about security vulnerabilities, see the Security Update Guide and the October 2025 Security Updates.Â
Windows Server, version 23H2 servicing stack update (KB5066779)Â - 25398.1906
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
Microsoft is not currently aware of any issues with this update.
How to get this update
Before you install this update
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.
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This update downloads and installs automatically from Windows Update and Microsoft Update. |
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Available |
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This update downloads and installs automatically from Windows Update for Business in accordance with configured policies. |
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Yes 1 |
To get the standalone package for this update, go to the Microsoft Update Catalog website. |
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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This update automatically syncs with Windows Server Update Services (WSUS) if you configure Products and Classifications as follows: Product: Microsoft Server operating system-21H2 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 InformationÂ
For a list of the files provided in this update, download the file information for cumulative update 5066780.
For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5066779) - version 25398.1906.Â
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