Microsoft Ships Emergency Windows Fix After September Update Breaks Three Things
Microsoft released emergency out-of-band updates on Sept. 14 to correct problems introduced by its September Patch Tuesday release. The September release patched nearly 1,000 flaws and was described as the company's biggest update ever. Reporting on the fix was published on Sept. 15. The Verge
The September update affected businesses, developers and gamers. That spread came from three separate failures. Folder shares on Hyper-V-based Linux virtual machines stopped working. Hyper-V is Microsoft's system for running virtual computers inside Windows. Sessions using Remote Desktop Services, the system that lets users log into another Windows machine over a network, were affected. Some USB audio devices, such as headsets, were affected. The Verge
Coverage for the correction is broad. On the client, the out-of-band update addresses Windows 11 versions 26H1, 25H2 and 24H2. Related out-of-band updates were released for Windows Server 2025 and 2022. Related updates were also released for the LTSC versions of Windows 10, the long-term support editions that avoid frequent feature change, and for Windows Server 2012 and Windows Server 2012 R2. The Verge
Two client packages define the Windows 11 fix. KB5129195 was released on Sept. 14, 2026 for Windows 11 versions 24H2 and 25H2, covering OS Build 26200.9457. KB5129194 was released on Sept. 14, 2026 for Windows 11 version 26H1, covering OS Build 28000.2956. Microsoft Support
Both packages list the same Hyper-V correction. KB5129195 fixed a Hyper-V known issue where applications using HCS-managed virtual machines, virtual machines handled by Microsoft's Host Compute Service, had trouble sharing host folders with Linux. KB5129194 fixed the same HCS-managed virtual machine issue for 26H1 systems sharing host folders with Linux.
The known issue was documented on Sept. 11, 2026. Microsoft added 'Host folder shares might be unavailable in Hyper-V-based Linux VMs' to KB5124008 for Windows 11 24H2 and 25H2 on that date. It added the same entry to KB5124012 for Windows 11 26H1 on that date. The support notes for KB5124008 and KB5124012 were originally published on Sept. 8, 2026.
Server servicing is moving in parallel. Microsoft released out-of-band update KB5129235 on Sept. 14, 2026 for Windows Server 2025. The Windows message center published a notice titled 'Take Action: Out-of-band update released to address issues from the September 2026 Windows security update.' The Windows release health hub notes that ACL hardening begins in October 2026.
The broader context here is scale and servicing cadence. A single cumulative package with close to 1,000 fixes touches virtualization plumbing, remote session paths and device connections at once. Out-of-band updates handle the exceptions. They ship targeted corrections without waiting for the next monthly cycle.
Looking at what this means for operations, triage is straightforward. Hyper-V host folder sharing and RDS session reliability can block development pipelines and remote administration. USB audio disruption matters for client fleets, but it rarely blocks builds or logins. In my view, that argues for patching virtualization hosts and session hosts first, then validating the client packages against standard images before wide deployment. Systems on LTSC and older Server releases merit the same order, with attention to maintenance windows.
Worth flagging for October is sequencing. An emergency fix in September followed by planned hardening in October rewards clean update rings and tested rollback. Shops that tighten imaging, backup and ring validation now will absorb the next change more easily. The long arc of Windows servicing favors recoverability. Fast correction beats perfect release.
