Remote Audio with RDP Broken After Installing Win11 Security Updates

^^ From my Win11 laptop pre-uninstall of the KB

^^ From my Win11 virtual machine pre-uninstall of the KB.

After I uninstalled, using PowerShell with the following command:
Remove-WindowsPackage -Online -PackageName "Package_for_RollupFix~31bf3856ad364e35~amd64~~26100.9168.1.19

The output of qwinsta on both machines look identical.
I verified remote audio worked when connected to my virtual machine via RDP after uninstalling.

I don't see anything that looks like a smoking gun in the Event logs. I was triggering events on the VM that would play audio (adjusting gmail and google chat notification sound settings) and then immediately looking at event logs on both PCs to see if a new warning / error event occurred but found nothing.

Hello @ChrisK-4772

Based on your testing, this does look like a potential regression associated with KB5121003, rather than a general RDP configuration or VM-side issue.

KB5121003 is the August 11, 2026 cumulative security update for Windows 11 24H2/25H2, bringing 24H2 to OS Build 26100.9168. However, Microsoft's current release notes state that Microsoft is not currently aware of any known issues with this update.

The strongest evidence here is your A/B testing:

• KB5121003 installed → RDP audio redirection fails across multiple target VMs.
• KB5121003 removed → audio redirection works.
• KB5121003 reinstalled → failure returns.
• Driver updates and RDP UDP/TCP changes don't resolve it.

That makes the Windows 11 client the common point of failure.

Before leaving the update uninstalled, I'd capture a few diagnostics while KB5121003 is installed. Check that the RDP client is still configured for:

Remote Desktop Connection → Local Resources → Remote audio → Settings → Play on this computer

Also verify that these services are running:

Get-Service Audiosrv, AudioEndpointBuilder

During an affected RDP session, check Device Manager and the remote session for the expected Remote Audio endpoint. It would also be useful to compare:

qwinsta

and Event Viewer logs under:

Applications and Services Logs → Microsoft → Windows → TerminalServices-*

between a working pre-KB5121003 state and the failing build.

Since you've already demonstrated reproducibility across multiple target VMs, I wouldn't spend much more time modifying the VM-side audio configuration. The next useful step is to report this through Feedback Hub from the affected Windows 11 machine and include the exact reproduction sequence:

Install KB5121003 → reboot → establish RDP session → Remote Audio missing/fails → uninstall KB5121003 → reboot → RDP audio restored.

If this is an enterprise-managed device, I'd also open a Microsoft support case and provide the Feedback Hub collection ID, affected OS build 26100.9168, RDP client version, Event Viewer traces, and confirmation that rollback consistently restores functionality.

For production machines, temporarily pausing deployment of KB5121003 on similarly affected systems may be a reasonable mitigation while the issue is investigated, but I wouldn't recommend permanently suppressing a cumulative security update. Microsoft may address a confirmed regression through a later cumulative or out-of-band update.

At the moment, I also wouldn't describe this as a Microsoft-confirmed KB5121003 issue, because the official release health information doesn't list RDP audio as a known problem yet. Your testing does, however, provide a strong case for reporting it as a reproducible regression.

Sharing this reference with you: Microsoft – August 11, 2026 KB5121003 release notes

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