Applications using Windows 10 or Windows 11’s built-in VPN client suddenly cannot connect.
Last Tuesday, Microsoft traditionally dropped numerous updates on Patch Tuesday (second Tuesday of the month) on all its platforms including Windows 10 and Windows 11. In addition to plugging a lot of security holes and other optimizations, the Windows update also broke the VPN service that comes standard with the operating system.
Several complaints on Reddit show problems with SonicWall and WatchGuard connections. The error message points to a failed L2TP connection attempt. The reason is a problem with the security layer during negotiation with a remote computer.
According to Bleeping Computer, not all VPN clients are affected by the Windows update. It is mainly those using the built-in VPN software of Windows 10 and Windows 11 that are experiencing problems.
IT admins can remove the specific Windows patch (KB5009543 and KB5008876) to fix the problem, even though in doing so they will lose the latest patches for other vulnerabilities. For now, the best advice seems to be to hold off on the update until Microsoft rolls out a patch that mitigates the problem. We always recommend testing updates internally first anyway to make sure there are no problems. After all, chances are that the VPN service used within your organization is not affected by the patch.
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