October 14, 2025—KB5066835 (OS Build 26100.6899)

Improvements

This security update contains fixes and quality improvements from KB5065426 (released September 9, 2025) and KB5068221 (released September 22, 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. ​​​​

• [App defaults]

  • New!  ​​We are rolling out some small changes in the European Economic Area (EEA) region for default browsers through the Set default button in Settings > Apps > Default apps:

    • Additional file and link types will be set for the new default browser, if it registers them.

    • The new default browser will be pinned to the Taskbar and Start menu unless you choose not to pin it by clearing the checkboxes.

    • There is now a separate one-click button for browsers to change your .pdf default, if the browser registers for the .pdf file type.

• [Narrator]

  • New!  The Screen Curtain feature in Narrator helps protect your privacy and improve focus by blacking out the screen while Narrator reads content aloud. This is especially helpful in public or shared spaces, where you can work with sensitive information without others seeing your screen. To turn on Narrator, press Ctrl + Windows + Enter. Then press Caps Lock + Ctrl + C to turn on Screen Curtain. While it’s on, you can use Narrator as usual with the screen hidden. Press Caps Lock + Ctrl + C again to turn it off.

  • New!  Narrator makes it easier to discover and learn about its features directly within the experience. Whether you're new or exploring advanced options, Narrator will guide you through the latest updates using a series of steps and prompts that explain each new feature and change.

• [Settings] 

  • New!  The country or region selected during device setup now appears under Settings > Time & language > Language & region.

  • Fixed: The storage card in Settings > System > About shows an incorrect or unreadable character instead of the proper disk size.

• [Taskbar & System Tray] 

  • New!  In addition to the new grouping of the Accessibility menu in Quick settings, there are text descriptions for the assistive technologies like Narrator, Voice access, and more for easier identification and learning.

  • New!  Adjusted the indicator (pill) under taskbar apps to make it wider and more visible.​​​​​​​

  • Fixed: WIN + CTRL + Number doesn't work anymore for switching windows of an open app in the taskbar.​​​​​​​

• [Windows Share]

  • ​​​​​​​New! When you share links or web content using the Windows share window, you'll see a visual preview for that content.

  • New!  In the Windows share window, you can select a compression level—High, Medium, or Low Quality—when editing and sharing images, instead of selecting from a 0–100 scale.

• [Color] Improved: Adjusted the location of the intensity and color boost sliders under Settings > Accessibility > Color Filters, so the color previews at the top of the page remain visible while adjusting the sliders. 

• [File Explorer] Improved: Performance has been enhanced when extracting archive files - this will particularly help in the case of copy pasting large numbers of files out of large 7z or .rar archives

• [Graphics]

  • Improved: Made underlying changes to enhance display related user experiences, including reducing screen flashing during certain display configuration transitions and eliminating unnecessary display resets that occurred in some cases​​​​​​​.

  • Fixed: Some displays might be unexpectedly green.

  • Fixed: If User Account Control (UAC) is set to Always Notify and the button under Settings > System > Display color calibration is selected for your display and canceled, Settings will stop responding.

• [Input] Fixed: Typing in Japanese with the touch keyboard might stop working after switching to typing with an English keyboard and then switching back.

• [Language] Fixed: After you install Windows Server 2025, you might see garbled or unreadable text in some feature names and descriptions in the Add Roles and Features wizard in Server Manager. This issue affects the Windows Admin Center Setup and Network ATC (Automatic Traffic Control) features in the Add Roles and Features wizard.

• [MSFTEdit.dll] Fixed: Some apps like Sticky Notes and dxdiag might stop responding when the display language is set to Arabic or Hebrew display.

• [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 KB5065426.

• [Quick Settings] Fixed: The top three buttons in the top row don’t respond when selecting to enable or disable them.

• [Performance] Fixed: This update addresses an issue to maintain efficiency of Storage Spaces Direct (S2D). When running complex software defined data center (SDDC) related workflows, it’s possible the system might become unresponsive.

• [Printing] Fixed: Printed lines might be unexpectedly thicker than expected.

• [Scripting] Fixed: Running a script on a remote Server Message Block (SMB) share might take an unexpectedly long time if the share is hosted on an older Windows Server version like Windows Server 2019.

• [Storage optimization] Fixed: An issue that prevented unused language packs and Feature on Demand packages from being fully removed, which led to unnecessary storage use and longer Windows Update installation times.

• [Windows Search]​​​​​​​

• This update addresses an issue that could cause Windows Search to successfully load very slowly, taking over 10 seconds to load before you can use it.

• Fixed: This update enhances the reliability of Windows Search and resolves an issue that prevented users from typing in Windows Search in some cases.
  
  Note: These fixes don't address an issue that might prevent Search from loading at all.

• [Windowing] 

  • ​​​​​​​Fixed: When you press ALT + Tab to switch out of a full screen app, other windows like Windows Terminal might stop responding.

  • Fixed: An underlying issue might lead to unexpected changes to window size and position after sleep and resume on some devices.

  • Fixed: Explorer.exe might stop working unexpectedly when a window is dragged, if window snapping is enabled.

• [Compatibility] 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, please refer to the Security Update Guide and the October 2025 Security Updates.

Known issues in 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.

Windows UpdateBusinessCatalogServer Update Services

Available	Next Step
	This update downloads and installs automatically from Windows Update and Microsoft Update.

File Information

For a list of the files provided in this update, download the file information for cumulative update 5066835. 

For a list of the files provided in the servicing stack update, download the file information for the SSU (KB5067630) - version 26100.6893.