Windows 11 updates break Always On VPN connections

Microsoft has confirmed that this month's security updates are breaking Always On VPN connections for some Windows 11 users. The affected updates are KB5124012 for Windows 11 26H1 and KB5124008 for Windows 11 25H2 and 24H2. A permanent fix is still in progress. Always On VPN is Microsoft's remote access technology, the successor to the older DirectAccess, and it is available on Windows 10, Windows 11, and Windows Server. 

It works with domain-joined, non-domain-joined, and Microsoft Entra ID-joined devices, supporting both the IKEv2 and SSTP tunneling protocols alongside multi-factor authentication, and it establishes its secure tunnel automatically in the background whenever a device connects to the internet.

What's going wrong

The problem, as per BleepingComputer, surfaces on Always On VPN profiles configured for automatic protocol selection, where the client tries IKEv2 first and falls back to SSTP if that connection fails. After installing the September update, that fallback process breaks. Affected connections can remain in a "Connecting" state or repeatedly attempt to connect without succeeding, and subsequent attempts can display the error "The specified port is already in use." Microsoft's alert was shared by Microsoft MVP Susan Bradley. In practice, an Always On VPN failure of this kind would keep affected devices from reaching internal company resources over the automatic tunnel until the workaround is applied.

Microsoft's workaround, for now

While Microsoft develops a permanent solution, it is telling IT administrators to change the Always On VPN profile from automatic protocol selection to a single protocol, either SSTP only or IKEv2 only, choosing based on their environment, security, and deployment requirements. Microsoft has not specified a particular management tool for making this change, so administrators should apply it through whichever method they already use to configure Always On VPN profiles.

This is one of several issues tied to the September 2026 cumulative updates. Over the past week, Microsoft has released emergency updates addressing Hyper-V issues, Remote Desktop Services failures, and USB audio problems also triggered by the same updates. It has also shared a workaround for a separate issue blocking some users from logging in with valid domain credentials, and said it is working to address a bug affecting the Windows File History backup feature.