"This issue can occur when the VPN is configured to automatically try another connection method if the initial connection fails (for example, when using automatic protocol selection with IKEv2 and SSTP)," Microsoft said.
Microsoft service alert seen by BleepingComputer and shared by Susan Bradley
Microsoft has notified IT administrators that users may experience Always On VPN connection issues after installing the September 2026 Windows 11 security updates. The service alert was seen by BleepingComputer and shared by Microsoft MVP Susan Bradley. In the advisory Microsoft said affected connections may remain stuck in a connecting state or repeatedly attempt and fail to connect.
Always On VPN: how the feature is supposed to behave
Always On VPN is a remote-access solution available on Windows 10, Windows 11, and Windows Server. It runs in the background and establishes a secure tunnel back to an organization's network automatically whenever a device connects to the internet. The feature replaces the legacy DirectAccess technology, supports domain-joined, non-domain-joined, and Microsoft Entra ID–joined devices, and lets administrators define which apps and services can use the VPN connection. Always On VPN supports modern tunneling protocols such as IKEv2 and SSTP and can enforce multi-factor authentication.
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End the scrambleSymptoms and a specific error message: 'The specified port is already in use.'
According to Microsoft, impacted VPN profiles that are configured to try alternate connection methods automatically may never complete the connection process. Affected VPN connections "might remain in a 'Connecting' state or repeatedly attempt to connect without succeeding." Microsoft also warned that subsequent connection attempts might display the error: "The specified port is already in use."
Mitigation: pick one tunneling protocol — SSTP only or IKEv2 only
While Microsoft works on a permanent fix, it provided a temporary workaround that requires IT administrators to remove automatic protocol selection from Always On VPN profiles. Specifically, organizations can mitigate the issue by changing the Always On VPN profile from automatic protocol selection to a single protocol — either "SSTP only" or "IKEv2 only" — and should choose the protocol that best fits their environment, security posture, and deployment requirements, Microsoft said.
What this means for IT administrators, enterprise users, and end users
- IT administrators: Review Always On VPN profiles for any configuration that uses automatic protocol selection and plan immediate profile changes to SSTP-only or IKEv2-only where appropriate. Expect to coordinate changes with device management and authentication teams because the workaround alters how clients establish tunnels.
- Enterprise users (device fleet managers and security teams): Test the single-protocol configuration across representative devices and applications before wide deployment to confirm compatibility with existing infrastructure and multi-factor authentication setups.
- End users: Be prepared for failed or repeatedly retrying VPN connections after the September 2026 Windows 11 security updates; report persistent "Connecting" states or the "The specified port is already in use." error to IT support so administrators can apply the mitigation.
This advisory arrives amid other disruptions tied to the September 2026 cumulative updates. Microsoft said one week ago it released emergency updates to fix Hyper-V issues, Remote Desktop Services failures, and USB audio problems also triggered by the September updates. The company also shared a temporary workaround for a separate issue that blocks some Windows 11 users from logging in with valid domain credentials and announced it is working to address a bug that may cause the built-in File History backup feature to stop working.
Microsoft is still working on a permanent solution for the Always On VPN problem; in the meantime, administrators must weigh compatibility and security when selecting a single tunneling protocol and roll that change out carefully across affected fleets.
Source: BleepingComputer — Microsoft: September Windows updates break Always On VPN connections
