Windows 11 September 2026 Update: KB5124008, KB5129195 & KB5124010 – What You Need to Know
Updated October 1, 2026 • Windows 11 24H2, 25H2 and 26H2
What Happened in September 2026?
September 2026 brought several Windows 11 updates in quick succession. Microsoft released KB5124008 on September 8, an out-of-band update KB5129195 on September 14, and the non-security preview update KB5124010 on September 22. Because the packages address different problems, users searching for the “September 2026 update” can encounter several KB numbers.
KB5124008: September 8, 2026 Security Update
KB5124008 is the September 8 cumulative security update for Windows 11 24H2 and 25H2. Microsoft lists builds 26100.9445 for 24H2 and 26200.9445 for 25H2.
The release notes document several issues associated with the September update, including Remote Desktop Services instability, USB Audio Class 1.0 problems, Hyper-V host-folder sharing issues and a File History backup problem. Later updates resolved several of these issues.
| Update | Date | Versions | Purpose |
|---|---|---|---|
| KB5124008 | Sep. 8, 2026 | 24H2 / 25H2 | Monthly cumulative security update |
| KB5129195 | Sep. 14, 2026 | 24H2 / 25H2 | Out-of-band fixes and security improvements |
| KB5124010 | Sep. 22, 2026 | 24H2 / 25H2 / 26H2 | Non-security preview and quality improvements |
Microsoft KB5124008 Update Catalog
KB5129195: The Out-of-Band Fix
Microsoft released KB5129195 on September 14 for Windows 11 24H2 and 25H2. It was released outside the normal monthly schedule and addressed an issue affecting Remote Desktop Services in some environments.
Affected systems could experience failed RDP connections, sign-in problems, or systems hanging during Remote Desktop configuration. Microsoft lists KB5129195 and later updates as the resolution.
The update also includes protection for CVE-2026-62721, which Microsoft describes as an elevation-of-privilege vulnerability involving Windows User-Mode Power Service.
Microsoft KB5129195 Update Catalog
KB5124010: September 22 Preview Update
KB5124010 is a non-security preview update for Windows 11 24H2, 25H2 and 26H2. It contains quality improvements and several user-facing changes.
File Explorer
- Improved preview behavior for downloaded HTML files.
- File Explorer Home remembers expanded and collapsed sections.
- Improved cloud-file thumbnail reliability.
- Fixes for an issue affecting the File Explorer address bar.
Touchpad
Additional precision-touchpad gestures were introduced, including single-finger scrolling from the left or right side and automatic scrolling.
Copilot key
On supported devices, the Copilot key can be remapped to Right Ctrl or the Context Menu key. Availability depends on the device and market.
File History
Microsoft states that this update fixes the File History problem in which some users could not create or update backups and could see a misleading “Reconnect your drive” message.
Known Problems and Their Fixes
File History backup failure
Some systems affected by KB5124008 could fail to create or update File History backups. Microsoft says this was resolved by updates released on and after September 22, including KB5124010.
Remote Desktop Services
Some organizations experienced RDP failures, sign-in problems or configuration hangs. KB5129195 addressed this issue.
USB audio
Some USB Audio Class 1.0 devices could fail to start or produce no sound after KB5124008. Microsoft documented a partial resolution in KB5129195 and subsequent servicing.
Hyper-V Linux VM shared folders
Some Plan9-based host-folder shares could become unavailable. Microsoft lists updates released from September 14 onward as resolving this issue.
Black screen or desktop loading
Microsoft also documents a black-screen or desktop-loading issue after sign-in affecting some environments, particularly certain Azure Virtual Desktop hosts using FSLogix. A temporary workaround is to open Task Manager with Ctrl + Shift + Esc, choose Run new task, enter explorer.exe, and run it.
How to Download the Updates Officially
Windows Update
- Open Settings.
- Go to Windows Update.
- Select Check for updates.
- Install the applicable cumulative update.
- Restart if requested.
Microsoft Update Catalog
For manual installation, use Microsoft's official catalog and select the package matching your Windows version and architecture.
How to Check Your Windows 11 Version
Press Win + R, type:
winver
and press Enter. You can also open Settings → System → About.
| Item | Example | Why it matters |
|---|---|---|
| Version | 24H2 / 25H2 / 26H2 | Determines applicable updates. |
| OS Build | 26100.xxxx | Shows the installed cumulative update level. |
| System type | x64 / ARM64 | Determines the correct standalone package. |
How to Install an MSU Update Manually
- Download the correct
.msupackage from Microsoft Update Catalog. - Open the file.
- Follow Windows Update Standalone Installer.
- Restart Windows if requested.
- Run
winveragain to confirm the build.
Advanced users can also use DISM, but Microsoft's package-specific installation order should be followed, especially where checkpoint cumulative updates are required.
DISM /Online /Add-Package /PackagePath:C:\Packages\update.msu
Windows 11 24H2 Home and Pro Support Ends Soon
Microsoft states that Windows 11 24H2 Home and Pro editions reach end of updates on October 13, 2026. After that date, those editions will no longer receive the normal monthly security and preview updates for that release. Enterprise and Education editions have a different servicing timeline and remain supported until October 12, 2027.
Users on 24H2 Home or Pro should check Windows Update and Microsoft's current release-health information for the upgrade path offered to their device.
Official Windows 11 Download Windows Release Health
Frequently Asked Questions
What is KB5124008?
It is the September 8, 2026 cumulative security update for Windows 11 24H2 and 25H2.
What is KB5129195?
It is the September 14, 2026 out-of-band cumulative update for Windows 11 24H2 and 25H2.
What is KB5124010?
It is the September 22, 2026 non-security preview update for Windows 11 24H2, 25H2 and 26H2.
Should I install the updates manually?
Most users should use Windows Update. Manual installation is useful when Windows Update fails or a standalone package is specifically required.
Is the File History problem fixed?
Microsoft states that the problem was resolved by updates released on and after September 22, including KB5124010.
When does Windows 11 24H2 Home and Pro reach end of support?
October 13, 2026.
Final Thoughts
The September 2026 Windows 11 update cycle is more complicated than a normal monthly update because Microsoft released several packages close together and used an out-of-band update to resolve important problems.
For most users, the practical workflow is simple: check winver, run Windows Update, and install the latest applicable cumulative update. If you need a standalone package, use Microsoft Update Catalog and match the Windows version and architecture exactly.