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Windows 11 23H2 Windows 11 23H2 Out-of-band update
Out-of-band Known issues

KB5129242

KB5129242: Cumulative update for Windows 11, version 23H2, September 2026. Remote Desktop failures and Linux shared-folder access fixed

In short

Addresses Remote Desktop instability, restores Plan9 host-folder access to Linux VMs, and resolves only 8-channel or 3D-mode symptoms for affected USB audio devices. Other USB audio symptoms remain.

Does it affect you? Applies to: This update is for Windows 11, version 23H2, on x64 and Arm64 devices. The Remote Desktop fix concerns affected RDS environments, the Plan9 fix concerns applications using HCS-managed virtual machines, and the audio issue is limited to USB Audio Class 1.0 devices.

Build
22631.7584
Restart
Required
Review notes Additional details from the official release notes (1) Read note
  • What changes The update resolves the USB Audio Class 1.0 symptoms for devices using 8-channel or 3D audio modes. Other audio symptoms are not resolved by this update.

The official sources are linked at the end of the page.

What changes

Fixes 3 changes

Remote Desktop Services

Verified in package

For: Environments using Remote Desktop Services

  • In affected environments, Remote Desktop connections and sign-ins might fail, servers might become unresponsive during Remote Desktop configuration, and related tools might stop responding.1
    Addresses instability after installing the September 2026 Windows security update KB5122880. Related tools include Microsoft Management Console (MMC), RDS Licensing Diagnoser, File Explorer, and the Windows Update page.

Hyper-V

For: Users of applications with HCS-managed virtual machines

  • Folders shared from a Windows host might now appear and be accessible in Linux virtual machines.2
    Fixes issues with sharing host folders using Plan9 in applications that use HCS-managed virtual machines.

Audio

Verified in package

For: Users of USB Audio Class 1.0 devices

  • Affected USB audio devices can use 8-channel or 3D audio modes without the issue described here. Other USB audio symptoms are not resolved by this update.3
    Partially resolves failures with USB Audio Class 1.0 devices using multichannel audio features, including 8-channel or 3D modes.

Improvement 1 change

Servicing stack

For: Devices installing Windows updates

  • The component that installs Windows updates receives quality improvements.4
    Includes servicing stack update KB5122879, build 22621.7578.

Known issues

  1. Resolved Affects: Everyone Resolved by KB5132059

    USB audio devices might fail to start or produce no sound

    Some USB Audio Class 1.0 devices might fail to start or produce audio, show Code 10, or have unresponsive volume controls or sound settings. This update resolves the symptoms when using 8-channel or 3D audio modes, but other symptoms remain unresolved.5

    How to apply the workaround Workaround

    For immediate help with symptoms not addressed by this update, IT administrators should contact Microsoft Support for Business.5

  2. Resolved Affects: Everyone Resolved by KB5126653

    File History might stop working after installing September 2026 Windows update

    Some customers using File History might be unable to create or update backups after the September 2026 Windows security update. This issue is resolved by updates released on and after October 13, 2026, such as KB5126653.6

    Resolution Fixed in KB5126653

    Install KB5126653 (or a later cumulative update) on affected devices. No manual workaround is required after updating.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2026-09-14
Classification
Updates
Type
Cumulative update
Restart
Required
Replaces
KB5122880, KB5120240, KB5099414, KB5093998
+56 earlier KB5087420, KB5082052, KB5078883, KB5075941, KB5078132, KB5077797, KB5073455, KB5071417, KB5070312, KB5068865, KB5067112, KB5066793, KB5065790, KB5065431, KB5064080, KB5066189, KB5063875, KB5062663, KB5062552, KB5060826, KB5060999, KB5062170, KB5058502, KB5058405, KB5055629, KB5058919, KB5055528, KB5053657, KB5053602, KB5052094, KB5051989, KB5050092, KB5050021, KB5048685, KB5046732, KB5046633, KB5044380, KB5044285, KB5043145, KB5043076, KB5041587, KB5041585, KB5040527, KB5040442, KB5039302, KB5039212, KB5037853, KB5037771, KB5036980, KB5036893, KB5035942, KB5035853, KB5034848, KB5034765, KB5034204, KB5034123
Replaced by
KB5126653
VersionBuildChannel
23H2 22631.7584 General availability

Security

No vulnerabilities are listed for this update.

Updated components

38 files changed since the previous update for the same versions.

Top changed componentsFiles
Audio2
Hyper-V and virtualization2
Remote Desktop2

Verified in package: changed files confirm Remote Desktop Services, Audio.

Sources

Updated
Cited passages from Microsoft's official notes (6)
  1. 1. In affected environments, RDS might become unstable, causing RDP connection and sign-in failures or servers to become unresponsive during Remote Desktop configuration. support.microsoft.com
  2. 2. Folders shared from the Windows host using Plan9 did not appear or could not be accessed in the guest environment. support.microsoft.com
  3. 3. This OOB update resolves the symptoms experienced on devices using 8-channel or 3D audio modes. support.microsoft.com
  4. 4. This update makes quality improvements to the servicing stack, which is the component that installs Windows updates. support.microsoft.com
  5. 5. This OOB update resolves the symptoms experienced on devices using 8-channel or 3D audio modes (last bullet point in the list of symptoms documented in this entry). learn.microsoft.com
  6. 6. This issue is resolved in Windows updates released on and after October 13, 2026 such as KB5126653. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 6 quoted passages · compared with Microsoft's page on Nov 9, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 4/5, clarity 4/5, completeness 4/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake