Microsoft has released KB5121003 for Windows 11 versions 24H2 and 25H2 as part of the August 2026 Patch Tuesday updates. The cumulative update installs Build 26100.9168 on version 24H2 and Build 26200.9168 on version 25H2. This update mainly focuses on security fixes and quality improvements to keep your PC safe and run smoothly. As part of Microsoft’s August 2026 Patch Tuesday release, KB5121003 addresses 3 zero-day vulnerabilities and approximately 400 flaws. In addition, Windows 11 KB5121003 includes Voice Isolation for Voice Access, support for compatible external fingerprint readers with Windows Hello Enhanced Sign-in Security (ESS), and File Explorer enhancements such as proper file size units (KB, MB, and GB) and middle-click support to open folders in a new tab. The update also resolves numerous issues affecting system performance, reliability, storage, printing, audio, networking, and overall Windows stability.
Note: Microsoft is rolling out some new features gradually through Controlled Feature Rollout (CFR), so they may not appear on every Windows 11 device immediately after installing KB5121003.
Let’s take a closer look at what’s new in Windows 11 KB5121003.
| Update Summary | Details |
|---|---|
| KB Number | KB5121003 |
| Build Numbers | 26200.9168 (25H2) / 26100.9168 (24H2) |
| Release Date | August 11, 2026 |
| Update Type | Security Update (Patch Tuesday) |
| Primary Focus | Security Fixes, Quality Improvements, New Features |
| Includes | Voice Isolation, external fingerprint reader support, File Explorer improvements, Windows Search enhancements, touchpad controls, and reliability fixes |
| Installation Required | Recommended |
| Restart Required | Yes |
What’s New in Windows 11 KB5121003 Update?
KB5121003 is primarily a security update, but it also includes several improvements and fixes previously available in the July preview update. This means users who skipped KB5101684 will receive these changes when they install the August cumulative update.
Key Highlights of KB5121003
- Better Windows Hello fingerprint support: Compatible external fingerprint readers can now work with Windows Hello Enhanced Sign-in Security (ESS).
- File Explorer improvements: File sizes in Details view are easier to read, with several Explorer reliability issues also addressed.
- File History fix: Fixes an issue that could incorrectly show an “invalid credentials” error when backing up files to an SMB network share.
- Improved power settings: Changes to display, sleep, hibernate, and other power options are applied more reliably across power plans.
- More fixes and improvements: KB5121003 also addresses issues affecting Windows Search, Taskbar, networking, printing, Remote Desktop, and other areas of Windows 11.
- Security fixes: KB5121003 addresses approximately 400 security vulnerabilities, including one actively exploited and two publicly disclosed zero-day vulnerabilities. It also includes fixes for 42 Critical vulnerabilities.
File Explorer Gets Some Useful Changes
One of the more noticeable changes in KB5121003 is File Explorer. Windows 11 now displays file sizes in the Details view using more appropriate units, such as KB, MB, or GB, instead of showing everything in KB. That makes it easier to understand the size of files at a glance.
Microsoft has also fixed several Explorer reliability problems involving Jump Lists, recent files, shared files, Task View, and multiple desktops.
There is another important fix for users who work with network drives. Files on DFS mapped drives could sometimes be incorrectly treated as downloaded from the internet after a computer restarted without a network connection. KB5121003 addresses that behavior.
File History Backup Error Is Fixed
If you use File History to back up files to a network share, this update may be particularly useful. Before KB5101684, Windows could show an “invalid credentials” error when connecting to an SMB network share even when the credentials were correct.
Microsoft has fixed this problem, so File History should be able to complete automatic backups normally in affected cases.
Windows Hello Gets Better Fingerprint Support
KB5101684 also adds support for compatible external fingerprint readers with Windows Hello Enhanced Sign-in Security. This is useful mainly for desktop PCs that do not have a built-in fingerprint sensor. If your fingerprint reader supports the required security features, you can set it up under:
Settings > Accounts > Sign-in options
Microsoft is rolling out this change gradually, so you may not see it immediately after installing the update.
Power Settings Should Behave More Reliably
The update also addresses several problems with Windows 11 power settings.
Changes made under Settings > System > Power & battery should now be applied more consistently across power plans. This includes settings for the display, sleep, hibernate, power button, sleep button, and closing a laptop lid.
Microsoft has also restored the ability to configure when Energy Saver automatically turns on.
For most users, this is the kind of fix you may only notice if your PC was previously ignoring a power setting.
Other Fixes in KB5101684
Microsoft has included several smaller fixes and improvements in KB5101684. Some are easy to miss, but they address problems that can affect everyday Windows 11 use.
- Windows Search: Microsoft fixed an issue that could cause Search to stop responding or behave unexpectedly in certain situations.
- Start menu and Taskbar: The update improves the reliability of the Start menu and Taskbar, including situations where Windows components may not load correctly after signing in.
- Remote Desktop: KB5101684 includes fixes for Remote Desktop and Azure Virtual Desktop environments, improving reliability when working in a remote Windows session.
- DHCP and network connections: Microsoft fixed a problem that could prevent Windows from renewing a DHCP lease correctly, particularly on devices using Modern Standby. This can help prevent certain network connection problems after the PC wakes up.
- IPPS printing: The update improves printing performance for printers that use Internet Printing Protocol Secure (IPPS).
- Magnifier: Microsoft changed the Magnifier experience on touch-enabled devices. The horizontal and vertical touch bars used for panning are now disabled by default because they could cover part of the magnified content. You can turn them back on under Settings > Accessibility > Magnifier.
- Mouse cursor settings: Windows 11 now does a better job of remembering the selected mouse cursor size after restarting or signing back into the PC.
- Windows sign-in and Lock screen: Microsoft has improved the reliability of the Windows sign-in process and Lock screen, including fixes for situations with low available memory.
- Dark mode system sounds: KB5101684 fixes an issue where some system sounds could be played incorrectly when Windows was using dark mode.
- Windows Update: Microsoft has improved how Windows calculates update progress and made changes to the cleanup process that runs after an update. These changes are intended to make updates complete more reliably and reduce the performance impact immediately after installation.
The update also includes KB5101711, a servicing stack update designed to improve the reliability of installing Windows updates. Microsoft currently lists no known issues for KB5101684.
Microsoft recommends installing KB5121003 as soon as possible to receive the latest security protections, reliability improvements, and bug fixes.
How to Install Windows 11 KB5121003 Update
KB5121003 is available through Windows Update, Microsoft Update, and the Microsoft Update Catalog. On most PCs, it will download and install automatically.
If you want to check manually:
- Press the Windows key + X, then select Settings. Go to Windows Update, then hit Check for updates.
- You should see the August 2026 cumulative update (KB5121003) (26200.9168) available for download.
- Click on the Download Now button to begin the process. Once done, reboot your computer to apply the changes.
- Windows 11 KB5121003 download offline installer
- Windows 11 KB5120240 download offline installer
The link above points to the Microsoft Update Catalog, a library of Windows Update offline installers.
- First, click on the ‘Download’ button next to the version of the OS installed on your machine.
- Next, run the .msu files to install the update.
- Once done, reboot your PC to apply the changes.
After the installation is complete, press Windows + R, type winver, and press Enter.
You should see one of the following build numbers:
| Windows version | Build after installing |
|---|---|
| Windows 11 24H2 | 26100.9168 |
| Windows 11 25H2 | 26200.9168 |
If you don’t see the update immediately, it may still be rolling out to your device. You can also install it manually using the offline installer from the Microsoft Update Catalog.
Troubleshooting: Windows 11 KB5121003 Fails to Install
If KB5121003 won’t install, gets stuck while downloading, or shows an installation error, try the following solutions in order. In most cases, one of these methods resolves the problem.
1. Restart Your PC and Check for Updates Again
Temporary Windows Update glitches can sometimes prevent cumulative updates from installing correctly.
- Restart your computer.
- Open Settings > Windows Update.
- Click Check for updates and try installing KB5121003 again.
2. Run the Windows Update Troubleshooter
Windows includes a built-in troubleshooter that can automatically detect and fix common update problems.
- Open Settings.
- Go to System > Troubleshoot > Other troubleshooters.
- Click Run next to Windows Update.
- Apply any recommended fixes and restart your PC.
3. Check Your Internet Connection and Free Disk Space
A slow internet connection or insufficient storage can interrupt the installation process.
- Make sure your internet connection is stable.
- Ensure the C: drive has at least 10 GB of free space for Windows Update to download and install files.
- Remove temporary files or uninstall unused apps if necessary.
4. Repair Corrupted System Files
Corrupted Windows system files are a common reason cumulative updates fail.
Open Command Prompt as Administrator and run:
sfc /scannowAfter it finishes, run:
DISM /Online /Cleanup-Image /RestoreHealthRestart your PC and try installing the update again.
5. Temporarily Disable Third-Party Antivirus
Some third-party antivirus or firewall programs can interfere with Windows Update.
Temporarily disable your security software, install KB5121003, and then enable the protection again after the installation finishes.
6. Install KB5121003 Using the Offline Installer
If Windows Update continues to fail, download the standalone installer from the Microsoft Update Catalog.
- Search for KB5121003.
- Download the package that matches your Windows version (24H2 or 25H2) and system architecture (x64 or ARM64).
- Double-click the downloaded .msu file.
- Restart your computer when prompted.
7. Note the Windows Update Error Code
If the installation still fails, check the error code shown in Windows Update (for example, 0x800f0922, 0x80070002, or 0x80073712). The error code usually points to the underlying cause and helps identify the correct solution.
Frequently Asked Questions
KB5121003 is the August 2026 Patch Tuesday cumulative update for Windows 11 versions 25H2 and 24H2. It includes important security fixes, quality improvements, and several new features designed to improve performance, accessibility, and overall system reliability.
Yes. KB5121003 is a mandatory security update released as part of Microsoft’s July 2026 Patch Tuesday. It includes security fixes, non-security improvements, and bug fixes.
After installing KB5121003, your Windows 11 version will be Build 26100.9168 (for 24H2) or Build 26200.9168 (for 25H2). You can confirm this by running winver.
Microsoft is using Controlled Feature Rollout (CFR) to gradually release some new features. As a result, certain features may not appear immediately on all devices even after the update is installed.
If the update won’t install, restart your PC and run the Windows Update Troubleshooter. If the problem continues, repair Windows system files using SFC and DISM, or install the update manually using the offline installer from the Microsoft Update Catalog. Checking the Windows Update error code can also help identify the cause of the problem.
Yes. You can uninstall it from Settings → Windows Update → Update history → Uninstall updates if you face any issues. However, uninstalling security updates is not recommended as a long‑term solution. Use it only for troubleshooting and reinstall the update when possible.
