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Windows Server 2025 Windows Server 2025 Security update
Patch Tuesday Zero-day

KB5066835

KB5066835: Cumulative update for Windows Server, version 2025, October 2025. Exploited Remote Access flaw patched; recovery USB issue remains

In short

Fixes actively exploited Windows flaws, including one in Remote Access Connection Manager, and adds security and usability changes. USB keyboards and mice might not work in the recovery environment.

Does it affect you? Applies to: Devices running Windows Server 2025, build 26100.6899. The update package is for x64 systems.

Build
26100.6899
Security
131 fixed · 2 critical · 3 exploited
Restart
Required
Review notes Additional details from the official release notes (2) Read notes
  • In detail On Windows Server 2025 domain controllers holding the schema master role, duplicate schema entries can cause schema mismatch errors and break replication across the Active Directory enterprise.
  • Known issues After installing KB5066835, USB keyboards and mice do not function in WinRE, preventing navigation of its recovery options. They continue to work normally in Windows.

The official sources are linked at the end of the page.

Microsoft publishes separate notes for this KB for Windows 11.

What changes

Fixes 18 changes

Settings

Verified in package
  • The storage card shows the disk size correctly instead of an unreadable character.1
    Settings > System > About

Taskbar & System Tray

  • The keyboard shortcut for switching between windows of an open taskbar app works again.2
    Fixes WIN + CTRL + Number.

Graphics

Verified in package 2 items
  • Some displays no longer turn unexpectedly green.3
  • Settings no longer stops responding when a display color calibration is canceled in the stated configuration.4
    Occurs when User Account Control is set to Always Notify and the calibration button under Settings > System > Display is selected and then canceled.

Input

For: Japanese touch keyboard users

  • Japanese touch keyboard typing works again after switching to English and back.5

Language

For: Windows Server 2025 administrators

  • Feature names and descriptions in the Add Roles and Features wizard no longer appear garbled or unreadable.6
    The issue affects Windows Admin Center Setup and Network ATC features in Server Manager's Add Roles and Features wizard.

MSFTEdit.dll

For: Devices using Arabic or Hebrew display languages

  • Some apps no longer stop responding when the display language is Arabic or Hebrew.7
    The page names Sticky Notes and dxdiag as examples.

Networking (known issue)

Verified in package

For: Devices using SMB v1 over NetBT

  • Access to shared files and folders works again in the affected setup.8
    Addresses an issue after KB5065426 when using SMB v1 over NetBIOS over TCP/IP (NetBT).

Quick Settings

Verified in package
  • The top three buttons in the first row respond when selected.9

Performance

For: Storage Spaces Direct users

  • Some complex data center workflows are less likely to leave the system unresponsive.10
    Addresses efficiency in Storage Spaces Direct (S2D) during complex software-defined data center workflows.

Printing

Verified in package
  • Printed lines no longer appear thicker than expected.11

Scripting

For: Devices running scripts from remote SMB shares

  • Scripts run faster from some remote shared folders.12
    Addresses slow scripts on remote SMB shares hosted on older Windows Server versions, such as Windows Server 2019.

Storage optimization

Verified in package
  • Unused language packs and optional feature packages are fully removed, reducing extra storage use and Windows Update installation time.13
    The packages are language packs and Feature on Demand packages.

Windows Search

Verified in package 2 items
  • Windows Search takes less time to load before it is ready to use.14
    Addresses loading delays that could exceed 10 seconds. This does not fix cases where Search fails to load at all.
  • Windows Search is more reliable, and typing in Search works in cases where it previously failed.15

Windowing

3 items
  • Other windows, including Windows Terminal, no longer stop responding when you switch away from a full-screen app.16
    Fixes the issue when using ALT + Tab.
  • Some devices keep their window sizes and positions after waking from sleep.17
  • File Explorer no longer stops working when a window is dragged with window snapping enabled.18
    The issue involved Explorer.exe.

Improvements 7 changes

Taskbar & System Tray

  • The indicator under open taskbar apps is wider and easier to see.19

Color

Verified in package

For: Color filter users

  • Color filter previews stay visible while you adjust the intensity and color boost sliders.20
    The sliders move under Settings > Accessibility > Color Filters.

File Explorer

2 items
  • Extracting archive files is faster, especially when copying many files from large archives.21
    Applies particularly to large 7z and .rar archives.
  • File previews are turned off for files downloaded from the internet to reduce the risk of opening unsafe content in preview.22
    The change applies automatically after installation. Microsoft's linked guidance explains how to unblock files.

Graphics

  • Some screen flashing and unnecessary display resets are reduced during display changes.23

Cryptography

For: Devices using RSA-based smart card certificates

  • RSA smart card certificates must use the newer key storage method. Some smart card sign-ins might be affected.24
    Requires Key Storage Provider (KSP) instead of Cryptographic Service Provider (CSP) for RSA-based smart card certificates. The page links resolution steps for authentication problems.

Servicing stack

  • The component that installs Windows updates receives quality improvements.25
    The cumulative update includes servicing stack update KB5067360, build 26100.6893.

New features 7 changes

App defaults

Gradual rollout
  • In the European Economic Area, choosing a default browser can also set more file and link types and pin it to Start and the taskbar.26
    The browser must register the file or link types. Clear the pinning checkboxes to prevent pins; a separate button can set the browser as the .pdf default.

Narrator

2 items

For: Narrator users

  • Screen Curtain blacks out the screen while Narrator reads aloud, helping keep visible content private.27
    Turn on Narrator with Ctrl + Windows + Enter, then toggle Screen Curtain with Caps Lock + Ctrl + C.
  • Narrator guides users through prompts that explain new features and changes.28

Settings

Verified in package
  • The country or region chosen during setup now appears in Language & region settings.29
    Settings > Time & language > Language & region

Taskbar & System Tray

Verified in package
  • Quick Settings adds text labels for accessibility tools, making them easier to identify.30
    The Accessibility menu groups assistive technologies such as Narrator and Voice access.

Windows Share

2 items
  • Shared links and web content now show a visual preview in the Windows share window.31
  • When editing and sharing images, you can choose High, Medium, or Low Quality compression.32
    The choices replace the 0–100 scale.

Removal 1 change

Compatibility

For: Devices using fax modem hardware that depends on ltmdm64.sys

  • Fax modems that depend on the removed driver no longer work.33
    The update removes the ltmdm64.sys driver.

Known issues

  1. Open Affects: Organizations and IT administrators

    Active Directory Replication

    On Windows Server 2025 domain controllers holding the schema master role, duplicate schema entries can cause schema mismatch errors. Replication then breaks across the entire Active Directory enterprise.34

    Workaround status No workaround yet

    Microsoft has not published a manual workaround for this issue yet. Monitor release health until a resolving update is available.

  2. Open Affects: Organizations and IT administrators

    Directory synchronization (DirSync)

    DirSync can incompletely sync on-premises Active Directory security groups with more than 10,000 members after the September 2025 security update.35

    Workaround status No workaround yet

    Microsoft has not published a manual workaround for this issue yet. Monitor release health until a resolving update is available.

  3. Open Affects: Organizations and IT administrators

    IIS websites might fail to load

    Microsoft says the reported IIS website loading issue does not affect Windows Server 2025. Server users do not need to take action.36

    Workaround status No workaround yet

    Microsoft has not published a manual workaround for this issue yet. Monitor release health until a resolving update is available.

  4. Open Affects: Organizations and IT administrators

    USB mouse and keyboard not working in the Windows Recovery Environment

    USB keyboards and mice might not work in the Windows Recovery Environment, preventing navigation of its recovery options. They continue to work normally in Windows.37

    Workaround status No workaround yet

    Microsoft has not published a manual workaround for this issue yet. Monitor release health until a resolving update is available.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2025-10-14
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5068221, KB5065426, KB5063878, KB5064489
+11 earlier KB5062553, KB5060842, KB5058411, KB5055523, KB5053598, KB5051987, KB5050009, KB5048667, KB5046617, KB5043080, KB5044284
Replaced by
KB5070773
VersionBuildChannel
2025 26100.6899 General availability

Security

131 vulnerabilities fixed
3 exploited 2 critical 129 important
VulnerabilitySeverityCVSS
CVE-2025-24990 Exploited
Windows Agere Modem Driver Elevation of Privilege Vulnerability
 Important 7.8
CVE-2025-59230 Exploited
Windows Remote Access Connection Manager Elevation of Privilege Vulnerability
 Important 7.8
CVE-2025-47827 Exploited
MITRE CVE-2025-47827: Secure Boot bypass in IGEL OS before 11
 Important 4.6
CVE-2025-49708
Microsoft Graphics Component Elevation of Privilege Vulnerability
 Critical 9.9
CVE-2016-9535
MITRE CVE-2016-9535: LibTIFF Heap Buffer Overflow Vulnerability
 Critical 4.0
CVE-2025-24052
Windows Agere Modem Driver Elevation of Privilege Vulnerability
 Important 7.8
CVE-2025-2884
Cert CC: CVE-2025-2884 Out-of-Bounds read vulnerability in TCG TPM2.0 reference implementation
 Important 5.3

The table lists the 7 exploited, publicly disclosed or critical vulnerabilities. See all 131 vulnerabilities →

Updated components

8,669 files changed since the previous update for the same versions.

Top changed componentsFiles
Settings138
Graphics and display61
Printing48
Bluetooth47
Networking45
Remote Desktop39
Security and sign-in37
Audio29
Windows Update27
File Explorer and shell26
Storage and file systems26
.NET networking23

Verified in package: changed files confirm Settings, Graphics, Networking (known issue), Quick Settings, Printing, Storage optimization, Windows Search, Color, Taskbar & System Tray.

Sources

Updated
Cited passages from Microsoft's official notes (37)
  1. 1. The storage card in Settings > System > About shows an incorrect or unreadable character instead of the proper disk size. support.microsoft.com
  2. 2. WIN + CTRL + Number doesn't work anymore for switching windows of an open app in the taskbar. support.microsoft.com
  3. 3. Fixed: Some displays might be unexpectedly green. support.microsoft.com
  4. 4. 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. support.microsoft.com
  5. 5. Typing in Japanese with the touch keyboard might stop working after switching to typing with an English keyboard and then switching back. support.microsoft.com
  6. 6. This issue affects the Windows Admin Center Setup and Network ATC (Automatic Traffic Control) features in the Add Roles and Features wizard. support.microsoft.com
  7. 7. Some apps like Sticky Notes and dxdiag might stop responding when the display language is set to Arabic or Hebrew display. support.microsoft.com
  8. 8. 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). support.microsoft.com
  9. 9. The top three buttons in the top row don’t respond when selecting to enable or disable them. support.microsoft.com
  10. 10. When running complex software defined data center (SDDC) related workflows, it’s possible the system might become unresponsive. support.microsoft.com
  11. 11. Printed lines might be unexpectedly thicker than expected. support.microsoft.com
  12. 12. 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. support.microsoft.com
  13. 13. 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. support.microsoft.com
  14. 14. 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. support.microsoft.com
  15. 15. This update enhances the reliability of Windows Search and resolves an issue that prevented users from typing in Windows Search in some cases. support.microsoft.com
  16. 16. When you press ALT + Tab to switch out of a full screen app, other windows like Windows Terminal might stop responding. support.microsoft.com
  17. 17. An underlying issue might lead to unexpected changes to window size and position after sleep and resume on some devices. support.microsoft.com
  18. 18. Explorer.exe might stop working unexpectedly when a window is dragged, if window snapping is enabled. support.microsoft.com
  19. 19. Adjusted the indicator (pill) under taskbar apps to make it wider and more visible. support.microsoft.com
  20. 20. 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. support.microsoft.com
  21. 21. 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. support.microsoft.com
  22. 22. This change is designed to enhance security by preventing a vulnerability when users preview potentially unsafe files. support.microsoft.com
  23. 23. 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. support.microsoft.com
  24. 24. This update enforces a security hardening improvement by requiring use of Key Storage Provider (KSP) instead of Cryptographic Service Provider {CSP) for RSA-based smart card certificates. support.microsoft.com
  25. 25. This update makes quality improvements to the servicing stack, which is the component that installs Windows updates. support.microsoft.com
  26. 26. Additional file and link types will be set for the new default browser, if it registers them. support.microsoft.com
  27. 27. To turn on Narrator, press Ctrl + Windows + Enter. Then press Caps Lock + Ctrl + C to turn on Screen Curtain. support.microsoft.com
  28. 28. Narrator makes it easier to discover and learn about its features directly within the experience. support.microsoft.com
  29. 29. The country or region selected during device setup now appears under Settings > Time & language > Language & region. support.microsoft.com
  30. 30. there are text descriptions for the assistive technologies like Narrator, Voice access, and more for easier identification and learning. support.microsoft.com
  31. 31. When you share links or web content using the Windows share window, you'll see a visual preview for that content. support.microsoft.com
  32. 32. you can select a compression level—High, Medium, or Low Quality—when editing and sharing images, instead of selecting from a 0–100 scale. support.microsoft.com
  33. 33. This update removes the ltmdm64.sys driver. Fax modem hardware dependent on this specific driver will no longer work in Windows. support.microsoft.com
  34. 34. This breaks replication in the entire Active Directory enterprise environment because the schema across domain controllers is now inconsistent. support.microsoft.com
  35. 35. can result in incomplete synchronization of large AD security groups exceeding 10,000 members. support.microsoft.com
  36. 36. Windows Server 2025 users don’t need to take action. support.microsoft.com
  37. 37. 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. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 37 quoted passages · compared with Microsoft's page on Oct 20, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 4/5, clarity 4/5, completeness 4/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake