Microsoft Issues Emergency Windows Patches for RDP, Hyper-V and USB Audio Bugs

Microsoft says some systems became unstable after the September 2026 Windows security updates. In affected Remote Desktop Services environments, RDP connections could fail after several minutes, sign-ins could fail, or systems could hang while configuring Remote Desktop. Related tools including Microsoft Management Console, RDS Licensing Diagnoser, File Explorer and the Windows Update page could also stop responding.

A separate regression affected applications using Host Compute Service-managed Linux virtual machines with Plan9 host-folder sharing. The virtual machines could still start, but folders shared from the Windows host might disappear or become inaccessible inside the guest. Microsoft’s release-health documentation specifically names Windows Subsystem for Linux and Claude Cowork among affected applications, while standard Hyper-V virtual machines that do not use Plan9 were not affected by that issue.

The audio situation needs a narrower reading than “Microsoft fixed USB audio.” Microsoft documents multiple symptoms affecting some USB Audio Class 1.0 devices after the September security update. The emergency release fixes the case where a device works in normal stereo but fails in 8-channel or 3D audio modes.

Other documented symptoms remain open: a device can still fail to start with Code 10 in Device Manager, produce no audio output, leave volume controls stuck or unresponsive, or make sound settings unavailable. Microsoft says it is working on those remaining cases. The issue is limited to USB Audio Class 1.0 devices; it should not be generalized to every USB headset, DAC or audio interface.

For Windows 11 versions 24H2 and 25H2, Microsoft’s out-of-band package is KB5129195, bringing those branches to builds 26100.9457 and 26200.9457 respectively. Windows 11 26H1 uses KB5129194. Windows 10 21H2 and 22H2 use KB5129236, and Microsoft has also issued corresponding fixes across affected Windows Server branches.

These are cumulative updates. Microsoft states that the out-of-band packages include the improvements and security protections from previous updates, so installing the applicable newer cumulative update does not require first installing the problematic September 8 rollup separately.