A week ago, Microsoft’s first patch day of 2022 (KB5009543) caused a number of clients and servers to experience problems connecting Windows 10 to VPN via the L2TP VPN protocol.
Users report that they go into the “Cannot establish a VPN connection. The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer”, error and mainly affects the built-in Windows VPN client when connecting to Ubiquiti Client-to-Site VPN, SonicWall, Cisco Meraki and WatchGuard firewalls.
Microsoft acknowledged the problem and said:
“After installing KB5009543, IP Security (IPSEC) connections that contain a Vendor ID may fail. VPN connections using Layer 2 Tunneling Protocol (L2TP) or IP Security Internet Key Exchange (IPSEC IKE) could also be affected.”
Now the company has released an out-of-band fix for the issue stating:
Out of band update to fix issues after installing Windows January update