Tracked Windows update
KB5124008 known issues and fixes
September 2026 security update for Windows 11 24H2 and 25H2. Resolves the tracked ARM launch issue and is associated with the Plan9 sharing and USB Audio Class 1.0 issues.
- Release date
- Windows versions
- Windows 11 24H2, Windows 11 25H2
- OS builds
- 26200.9445, 26100.9445
- Official source
- KB5124008 — Microsoft Support
- Last verified
This is a directory of TraceCheck's tracked records, not a complete list of every vendor issue. Zero tracked records does not establish that an update is problem-free.
TraceCheck cross-reference
What role does this KB play?
Keep the update linked to the failure separate from the update linked to its resolution. These roles come from the cited issue records.
| Issue | This KB's role | Evidence |
|---|---|---|
| USB Audio Class 1.0 Code 10 / no sound after KB5124008 | Originating update | Microsoft [1] · Microsoft [2] · Microsoft [3] |
| Claude Cowork / WSL host folders missing after KB5124008 | Originating update | Source: Microsoft |
| Teams / new Outlook fail to launch on ARM after KB5121003 | Resolving update | Source: Microsoft |
An originating update identifies the documented association; it does not establish the technical root cause. A resolving update applies to its listed Windows versions. This historical index does not identify today's latest update.
Known issues
Mitigated Tracked software issue
USB Audio Class 1.0 Code 10 / no sound after KB5124008
Microsoft tracks a USB Audio Class 1.0 failure affecting startup, sound and controls. The current vendor state is mitigated. On Windows 11 24H2/25H2, KB5129195 fixes the 8-channel/3D audio subset; it does not establish that Code 10 or every no-sound symptom is resolved.
15 documented versions across Windows 11, Windows 10, Windows Server · Affected environments
Recorded update fix: Partial — remaining symptoms unresolved · Windows 11 24H2, Windows 11 25H2 · Check instructions
Resolved issues
Resolved Resolution recorded 2026-09-14
Claude Cowork / WSL host folders missing after KB5124008
Microsoft confirmed a Plan9 host-folder sharing failure in HCS-managed Linux VMs after the September 2026 Windows security update. Claude Cowork and WSL are named examples. For Windows 11 24H2/25H2, KB5129195 and subsequent updates resolve the issue; ordinary Hyper-V VMs without Plan9 are outside this documented scope.
6 documented versions across Windows 11, Windows 10 · Affected environments
Recorded update fix: Documented symptom resolution · Windows 11 24H2, Windows 11 25H2 · Check instructions
Resolved Resolution recorded 2026-09-08
Teams / new Outlook fail to launch on ARM after KB5121003
Microsoft confirmed launch failures or unexpected exits in Teams and the new Outlook on ARM devices after the August 2026 security update. New or freshly imaged PCs without Store updates are more likely to be affected. Windows 11 24H2/25H2 updates from KB5124008 onward resolve this documented issue.
Windows 11 26H1; Windows 11 25H2 · KB5121003; Windows 11 24H2 · KB5121003
Recorded update fix: Documented symptom resolution · Windows 11 24H2, Windows 11 25H2 · Check instructions
Compatibility reports
No separate unconfirmed compatibility reports are currently tracked.
Related fixes and workarounds
Update for the 8-channel / 3D audio subset
FACT Official fix · vendor fix
KB5129195 corrects the multichannel subset on Windows 11 24H2/25H2. Other documented startup, no-sound and control symptoms remain outside this partial resolution. The cited update is historical; select the applicable current update for the device.
Partial fix — remaining symptoms are unresolved
Applies to: Windows 11 24H2, Windows 11 25H2.
Risk: medium (TraceCheck editorial assessment, not a vendor success rate)
Install the applicable Windows update for Plan9 sharing
FACT Official fix · vendor fix
Microsoft documents KB5129195 or subsequent updates for Windows 11 24H2/25H2. Use the current applicable cumulative update. Previous Group Policy mitigation also requires the vendor re-enable/install/restart procedure. Other host versions need their own packages.
Documented symptom resolution
Applies to: Windows 11 24H2, Windows 11 25H2.
Risk: medium (TraceCheck editorial assessment, not a vendor success rate)
Fixing update: KB5129195 · Microsoft [1] · Microsoft [2]
Read Microsoft's instructions ↗Read Microsoft's instructions ↗
Install the applicable Windows update for ARM app launches
FACT Official fix · vendor fix
Microsoft records the resolution in KB5124008 and later Windows 11 24H2/25H2 updates. The linked package is historical, not necessarily the latest applicable update. This package scope excludes 26H1.
Documented symptom resolution
Applies to: Windows 11 24H2, Windows 11 25H2.
Risk: medium (TraceCheck editorial assessment, not a vendor success rate)
Store-package workaround for affected pre-September 8 devices
FACT Official workaround · workaround
For affected devices on a Windows update predating September 8, open Microsoft Store, select Downloads, check for updates, and install Auto Super Resolution Package version 1.0.19.0 or later. Microsoft says this workaround is unnecessary after the Windows resolution.
Documented symptom resolution
Applies to: Windows 11 24H2, Windows 11 25H2, Windows 11 26H1.
Risk: low (TraceCheck editorial assessment, not a vendor success rate)
Evidence
- KB5124008 — Microsoft Support
Microsoft · Vendor documentation
Supports: Release date, Windows 11 24H2/25H2 applicability and OS builds. This KB is a historical record, not a claim about the latest update.
Change history
No earlier verified state transitions are recorded.