October 14, 2025—KB5066837 (OS Build 10240.21161)
Applies To
Release Date:
14/10/2025
Version:
OS Build 10240.21161
Windows Secure Boot certificate expirationÂ
Important: 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.
Windows updates do not install Microsoft Store application updates. If you are an enterprise user, see Microsoft Store apps - Configuration Manager. If you are a consumer user, see Get updates for apps and games in Microsoft Store.
Support for Windows 10 has ended on October 14, 2025
After October 14, 2025, Microsoft will no longer provide free software updates from Windows Update, technical assistance, or security fixes for Windows 10. Your PC will still work, but we recommend moving to Windows 11.​​​​​​​​​​​​​​​​​​​​​
Summary
This article lists the security issues and quality improvements included in this security update.
Windows 10, version 1507
This security update includes fixes and quality improvements that are part of the following update:
The following is a summary of the issues that this update addresses. The bold text within the brackets indicates the item or area of the change we are documenting.
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[Fax modem driver] This update removes the ltmdm64.sys driver. Fax modem hardware dependent on this specific driver will no longer work in Windows.
If you installed earlier updates, only the new updates contained in this package will be downloaded and installed on your device.
For more information about security vulnerabilities, please refer to the new Security Update Guide website and the October 2025 Security Updates.
For information about Windows update terminology, see the article about the types of Windows updates and the monthly quality update types. For an overview of Windows 10, version 1507, see its update history page.
Known issues in this update
We are currently not aware of any issues with this update.
How to get this update
Before you install this update
To install any Windows 10, version 1507 cumulative update released on or after January 14, 2025, we recommend you first install the latest Servicing Stack Update (SSU). If your device or offline image does not have the latest SSU installed, you might not be able to install this update.
Caution Until you install the latest SSU, this update might not be offered to your device. To reduce your security risk, install the SSU as soon as possible.
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If you use Windows Update, the latest SSU (KB5066587) will be offered to you automatically. If the latest SSU is not installed, you might not be able to install this update.
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If you use Windows Update for Business, the latest SSU (KB5066587) will be offered to you automatically. If the latest SSU is not installed, you might not be able to install this update.
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If you use the Update Catalog, we recommend you download and install the latest SSU (KB5066587). If the latest SSU is not installed, you might not be able to install this update.
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If you are a Windows Server Update Services (WSUS) administrator, you must approve SSU KB5066587 and this update KB5066837.
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 will be downloaded and installed automatically from Windows Update and Microsoft Update. |
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This update will be downloaded and installed automatically from Windows Update for Business in accordance with configured policies. |
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To get the standalone package for this update, go to the Microsoft Update Catalog website. For information about how to download and install updates from the Update Catalog, see How to download updates that include drivers and hotfixes from the Windows Update Catalog. |
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This update will automatically sync with Windows Server Update Services (WSUS) if you configure Products and Classifications as follows: Product: Windows 10 Classification: Security Updates |
File information
A list of the files that are included in this update are provided in a CSV (Comma delimited) (*.csv) file. The file can be opened in a text editor such as Notepad or in Microsoft Excel.
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