Unexpected cumulative update KB5129195 (Build 26300.9457) for Windows 11, version 26H2 (2026 Update) closes a privilege escalation vulnerability, restores stability of RDP connections and multichannel audio on USB Audio Class 1.0 devices. The cumulative package is intended for Windows 11, version 26H2, based on x64 (amd64) and ARM64 processors. The update is cumulative and includes all security fixes and improvements from previous releases.
Unexpected cumulative update KB5129195 (Build 26300.9457) for Windows 11, version 26H2, closes a privilege escalation vulnerability in the power management service and eliminates failures that appeared after the September release: RDP connection drops, errors accessing host computer folders in Hyper-V, and loss of multichannel audio on USB Audio Class 1.0 devices. The update is cumulative and includes all security fixes and improvements from the September 8, 2026 security update (KB5124008), as well as the changes listed below.
- Security. A privilege escalation vulnerability in the Windows User-Mode Power Service (UMPS) has been closed – CVE-2026-62721.
- Remote Desktop. Instability of Remote Desktop Services (RDS) has been fixed, which after installing the September update caused RDP connection drops, sign-in errors, and server hangs.
- Hyper-V. Access to host computer folders and shared resources of Linux virtual machines that connect via the Plan 9 protocol has been restored.
- Audio. Support for multichannel and surround sound on USB Audio Class 1.0 devices has been restored.
Known issues. On some USB Audio Class 1.0 devices, audio may disappear, and Error Code 10 appears in Device Manager. Microsoft is working on a fix. If you installed previous updates, only the new updates contained in this package will be downloaded and installed.
Update KB5129195 is downloaded and installed automatically through Windows Update. To check, go to Settings > Windows Update and click Check for updates.
| Increase or Decrease in Performance | Optimization | PC Speed | Gaming Optimization |
|---|---|---|---|
| ⚪ No direct performance change (security fix, not a performance feature) | 🟢 Minor optimization — closes a privilege escalation hole in UMPS, reducing attack surface rather than speeding up the system | ⚪ No measurable impact on overall PC speed | ⚪ No impact on gaming performance |
| 🟢 Moderate increase in stability (not raw performance) — RDP connection drops and server hangs fixed, so remote sessions no longer stall | 🟢 High optimization for RDS reliability — sign-in errors and hangs eliminated, restoring normal remote workflow | 🟡 Slight perceived speed gain for remote users — fewer disconnects and retries make RDP feel faster | ⚪ No impact on gaming performance |
| 🟢 Increase in VM performance — restored access to host folders and Plan 9 shared resources for Linux VMs, removing I/O stalls | 🟢 High optimization for Hyper-V Linux guests — shared resource access works again without workarounds | 🟡 Moderate speed gain inside affected VMs — file and resource access no longer blocks | ⚪ No direct gaming impact, but VM-based game servers or test environments benefit |
| 🟢 Increase in audio functionality (not raw performance) — multichannel and surround sound on USB Audio Class 1.0 devices restored | 🟢 Moderate optimization — correct multichannel output restored, no more downmixing to stereo | ⚪ No impact on PC speed | 🟡 Slight gaming benefit — proper surround sound for games using USB Audio Class 1.0 |
| 🔴 Decrease in performance/functionality for some users — audio may disappear on certain USB Audio Class 1.0 devices (Error Code 10) | 🔴 Negative optimization — known issue, fix pending from Microsoft | ⚪ No impact on PC speed | 🔴 Potential gaming regression — loss of audio on affected USB headsets/DACs |
Find and Change Settings
| Setting | Where to find | How to change |
|---|---|---|
| USB Audio Class 1.0 Multichannel and Surround Sound | Settings > System > Sound | Open Settings > System > Sound. Under Output, select your USB Audio Class 1.0 device. In the device properties, set the audio format and enable multichannel or surround sound if the restored support is available for your device and driver. |
| USB Audio Device Error Code 10 | Device Manager > Sound, video and game controllers | Open Device Manager, expand Sound, video and game controllers, and check the USB Audio Class 1.0 device for Error Code 10. If the error appears, update the device driver or reinstall it. Microsoft is working on a fix, so also check Windows Update for newer updates. |
| Windows Update Package Installation | Settings > Windows Update | Open Settings > Windows Update and select Check for updates. If previous updates were already installed, only the new updates contained in this package will be downloaded and installed. |
Official announcement on the Microsoft website.
The last 10 Windows updates:
| Update | Build | Version | Windows | Channel | Date |
|---|---|---|---|---|---|
| KB5124006 | 28000.3086 | 26H1 | Windows 11 | Preview | 2026-09-22 |
| KB5124010 | 26200.9550 | 26H2 | Windows 11 | Preview | 2026-09-22 |
| KB5124138 | 28120.3032 | 26H1 | Windows 11 | Experimental | 2026-09-18 |
| KB5124140 | 26220.9492 | 25H2 | Windows 11 | Beta | 2026-09-18 |
| KB5124137 | 26340.9502 | 26H2 | Windows 11 | Experimental | 2026-09-18 |
| KB5129242 | 22631.7584 | 23H2 | Windows 11 | Stable | 2026-09-14 |
| KB5129236 | 19045.7727 | 22H2 | Windows 10 | Stable | 2026-09-14 |
| KB5129195 | 26300.9457 | 26H2 | Windows 11 | Stable | 2026-09-14 |
| KB5129194 | 28000.2956 | 26H1 | Windows 11 | Stable | 2026-09-14 |
| KB5124115 | 26220.9472 | 25H2 | Windows 11 | Beta | 2026-09-11 |