September Windows 11 Security Update KB5124008 Breaks Always On VPN Certificate Authentication
The September security update KB5124008 for Windows 11 has introduced a regression that disables Always On VPN connections using certificate-based authentication.
The issue affects devices running Windows 11 versions 24H2 and 25H2 that connect to Remote Routing and Access Service (RRAS) and Network Policy Server (NPS) instances on Windows Server 2019. VPN profiles deployed via Microsoft Intune are impacted, with the failure occurring during the certificate negotiation phase of the IPsec connection.
Users confirm the problem is reproducible: the VPN works before the patch, stops after installation, and resumes after patch removal and reboot. An independent Microsoft consultant suggested the update altered the network stack or IPsec certificate handling.
Microsoft has not yet acknowledged the regression or released a fix. Administrators are advised to pause deployment through WSUS or Intune and open support cases with client and NPS logs. A potential workaround involves switching profiles to EAP-TLS, though its reliability remains unconfirmed.
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