Microsoft has released an emergency out-of-band update for Windows 11 after the September 2026 security update caused a number of serious problems for some users and organizations.
The new KB5129195 update is rolling out for Windows 11 24H2 and 25H2, bringing the operating system to Build 26100.9457 and 26200.9457, respectively. Unlike a normal monthly update, this is an out-of-band release specifically designed to address problems introduced by the September 8 security update.
The emergency release is particularly important for users relying on Remote Desktop, Hyper-V-based Linux environments, or certain USB audio devices.
Windows 11 KB5129195 fixes Remote Desktop problems
One of the biggest problems caused by the September update involved Remote Desktop Services (RDS).
On affected systems, Remote Desktop connections could fail after several minutes, users could encounter sign-in problems, or systems could become stuck at the “Please wait for the Remote Desktop Configuration” screen.
Other Windows components could also become unresponsive, including File Explorer, Microsoft Management Console and parts of the Windows Update interface.
For businesses and remote workers, this was more than a minor inconvenience. A broken RDS connection can effectively prevent users from accessing remote PCs and servers.
KB5129195 addresses this issue, giving affected Windows 11 systems a permanent fix without requiring administrators to remove the September security update.
Hyper-V and Linux sharing problems are also fixed
The September update also introduced a problem with applications using HCS-managed virtual machines and Plan9 folder sharing.
In affected environments, folders shared from the Windows host could disappear from Linux virtual machines or become inaccessible.
This could affect applications and development environments that rely on those shared folders. Microsoft specifically lists WSL and Claude Cowork among the affected applications.
The important part is that Microsoft has now resolved this problem in updates released from September 14 onward, including KB5129195.
Standard Hyper-V virtual machines that don’t use the affected Plan9 sharing feature are not impacted by this particular issue.
USB audio problems get a partial fix
KB5129195 also tackles an audio problem affecting certain USB Audio Class 1.0 devices.
After installing the September security update, some devices could continue working normally in stereo but fail when users switched to multichannel audio configurations such as 8-channel or 3D audio.
Microsoft says KB5129195 fixes those multichannel audio problems.
However, the audio fix is not complete.
Some affected PCs may still experience more serious symptoms, including no audio output, unresponsive volume controls or a Code 10 error in Device Manager. Microsoft says it is continuing to work on those remaining problems.
So, if your Windows 11 PC completely lost audio after the September update, KB5129195 may not solve everything yet.
KB5129195 also includes an important security fix
The emergency update isn’t only about repairing broken features.
Microsoft has also included additional protections related to CVE-2026-62721, an elevation-of-privilege vulnerability affecting the Windows User-Mode Power Service.
That makes KB5129195 more significant than a simple bug-fixing patch. Users get the emergency compatibility and reliability fixes alongside an additional security improvement.
What KB5129195 does not fix
Although the emergency update addresses several major problems, it doesn’t mean every issue reported after the September update has disappeared.
Some separate Windows 11 problems remain under investigation, including reports involving certain Explorer.exe crashes, File History behavior and AMD GPU-related problems. These issues are not listed as fixes in KB5129195.
This is an important distinction: KB5129195 fixes specific problems that Microsoft has acknowledged, rather than serving as a complete reset for every issue caused by the September update.
Should you install Windows 11 KB5129195?
For Windows 11 24H2 and 25H2 users, installing KB5129195 is recommended, particularly if you experienced problems with Remote Desktop, Hyper-V-based Linux environments or multichannel USB audio following the September update.
The update is a cumulative out-of-band release and includes the relevant fixes from the previous security update.
You can check for it through:
Settings → Windows Update → Check for updates
Look for:
2026-09 Security Update (KB5129195)
If your PC has been working normally, the update is still important because it contains security protections in addition to the reliability fixes.
Windows 11 September update gets an important course correction
The September 2026 Windows 11 update was supposed to deliver security improvements and several long-awaited changes, but the problems that followed forced Microsoft to release an emergency patch only days later.
KB5129195 represents Microsoft’s response to some of the most disruptive issues, particularly those affecting Remote Desktop, Hyper-V/Linux folder sharing and multichannel USB audio.
The fix is welcome, although users dealing with the remaining audio, Explorer or other unrelated problems may still have to wait for additional updates.
For now, if your Windows 11 PC was affected by the September update, KB5129195 is the patch to look for.
For the latest rollout updates and troubleshooting guides, follow our Windows 11 coverage as more details emerge.
