Windows 11 September 2025 Update (KB5065426): What’s New in Build 26100.6584

Microsoft has officially rolled out its September 2025 Patch Tuesday update for Windows 11 version 24H2, delivering the cumulative update KB5065426. This release upgrades systems to OS Build 26100.6584, focusing on critical security patches, quality improvements, and refreshed AI components for Copilot+ PCs.

If you’re running Windows 11—whether on a personal device or across enterprise infrastructure—this update is an essential install. Here’s a breakdown of what KB5065426 brings, how it affects security and features, and step-by-step guidance for installation.

Why KB5065426 Matters

• Security-focused release: This is primarily a cumulative security update, incorporating both September fixes and improvements from August’s optional preview.
• Secure Boot deadlines ahead: Microsoft reminds users that most Secure Boot certificates expire in June 2026, urging IT admins and power users to prepare now.
• AI component refresh for Copilot+ PCs: AI-driven features like Image Search, Content Extraction, Semantic Analysis, and the Settings Model are updated to v1.2508.906.0, but only on Copilot+ hardware.

Key Fixes and Improvements in KB5065426

Microsoft highlights several important bug fixes and enhancements:

• MSI repair and UAC prompts – Fixes unexpected User Account Control requests during Windows Installer repairs. IT admins can now allowlist apps to bypass UAC in these cases.
• SMB readiness auditing – Adds logging to help IT assess SMB client compatibility with Server Signing and Extended Protection for Authentication (EPA) ahead of stricter security enforcement.
• Input method reliability – Resolves app hangs related to certain input method scenarios.
• IIS Manager modules – Restores missing Internet Information Services modules that previously blocked configuration via the UI.
• NDI audio stability – Fixes stuttering in apps using Network Device Interface (NDI), such as OBS Studio with Display Capture, after August’s update.

This release also includes the Servicing Stack Update (SSU) KB5064531 (Build 26100.5074), ensuring reliable update delivery.

New Features Rolling Out Gradually

Alongside fixes, Microsoft is staging several Windows 11 24H2 features, which may take time to reach all devices:

• Expanded Notification Center clock with seconds.
• Lock screen widgets with reordering options.
• Grid view for image results in Windows Search.
• A revamped Widgets board with multiple dashboards.
• Updated visuals for Windows Hello sign-in.
• On Copilot+ PCs: a new Recall homepage and interactive Click to Do tutorial.

⚠️ Note: These features are controlled via Microsoft’s servers. You may not see them immediately after installing KB5065426.

Known Issues: PSDirect Failures on Hotpatch Systems

Some devices using Hotpatch may experience PowerShell Direct (PSDirect) connection failures when host and guest VMs are mismatched in updates. Logs may show Security Event ID 4625.

Workaround: Install the follow-up update KB5066360 on both host and guest machines to restore functionality.

How to Install KB5065426

You can install this update using multiple methods:

1. Windows Update (easiest)

• Go to Settings > Windows Update > Check for updates.
• The update downloads and installs automatically.

2. Microsoft Update Catalog

• Download KB5065426 directly from the Microsoft Update Catalog.

3. DISM (for IT admins and advanced users)

Install on a running PC:

DISM /Online /Add-Package /PackagePath:C:\Packages\Windows11.0-KB5065426-x64.msu

Add to an offline image:

DISM /Image:C:\mountdir /Add-Package /PackagePath:C:\Packages\Windows11.0-KB5065426-x64.msu

When multiple MSUs are required, follow Microsoft’s recommended order:

1. windows11.0-kb5043080-x64_*.msu
2. windows11.0-kb5065426-x64_*.msu

Can You Uninstall KB5065426?

• The LCU (Latest Cumulative Update) can be removed with DISM, but the SSU (Servicing Stack Update) is permanent.
• To remove KB5065426:

DISM /Online /Get-Packages
DISM /Online /Remove-Package /PackageName:Package_for_RollupFix~31bf3856ad364e35~amd64~~26100.6584.1.x

• Running wusa.exe /uninstall will not work since SSUs cannot be removed.

Troubleshooting Installation Errors

If KB5065426 fails to install:

• Ensure you have enough free disk space.
• Avoid powering off during the first reboot.
• Try a repair install via “Fix problems using Windows Update” to preserve apps and files.
• Run repair commands:

DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow

Windows Server 2025 Notes

The same update (KB5065426) applies to Windows Server 2025, delivering the same security patches plus server-specific fixes:

• Taskbar policy to prevent repinning apps.
• Mouse accessibility enhancements.
• BitLocker reliability on removable media.
• Networking profile improvements on domain controllers.
• USB reconnect fix after sleep.
• Removal of PowerShell 2.0.

Security Release Details

For a complete list of CVE vulnerabilities, severities, and exploitability ratings, see Microsoft’s Security Update Guide.

Conclusion

The September 2025 Patch Tuesday update (KB5065426) is a must-install for Windows 11 24H2 and Windows Server 2025 users. It delivers vital security fixes, AI enhancements for Copilot+ hardware, and reliability improvements across system components.

Whether you’re an everyday user or an enterprise IT admin, updating now ensures protection against vulnerabilities and smoother system performance. And if you’re waiting for new UI features like the expanded clock, lock screen widgets, or Recall enhancements, keep in mind they’re rolling out gradually.

👉 Bottom line: Install KB5065426 as soon as possible to stay secure, benefit from under-the-hood improvements, and prepare your device for upcoming Windows innovations.