Microsoft release out-of-band fix for Windows 10 “Can’t connect to VPN. The L2TP connection attempt failed” error

A week ago Microsoft’s first Patch Tuesday of 2022 (KB5009543 ) caused issues for Windows 10 connecting to VPN for a number of clients and servers over the L2TP VPN protocol.

Users are reporting running into the  “Can’t connect to VPN. The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer,” error, and is mainly affecting the built-in Windows VPN client when connecting to Ubiquiti Client-to-Site VPN, SonicWall, Cisco Meraki, and WatchGuard Firewalls.

Microsoft  confirmed the issue, saying:

“After installing KB5009543, IP Security (IPSEC) connections which contain a Vendor ID might fail. VPN connections using Layer 2 Tunneling Protocol (L2TP) or IP security Internet Key Exchange (IPSEC IKE) might also be affected.”

Now the company has released an out-of-band fix for the issue, saying:

Out-of-band update to address issues after installing the January Windows update

Microsoft is releasing Out-of-band (OOB) updates today, January 17, 2022, for some versions of Windows. This update addresses issues related to VPN connectivity, Windows Server Domain Controllers restarting, Virtual Machines start failures, and ReFS-formatted removable media failing to mount. All updates are available on the Microsoft Update Catalog, and some are also available on Windows Update as an optional update. Check the release notes for your version of Windows for more information.

Updates for the following Windows versions are available on Windows Update as an optional update. For instructions, see the KB for your OS listed below:

• Windows 11, version 21H1 (original release): KB5010795
• Windows Server 2022: KB5010796
• Windows 10, version 21H2: KB5010793
• Windows 10, version 21H1: KB5010793
• Windows 10, version 20H2, Windows Server, version 20H2: KB5010793
• Windows 10, version 20H1, Windows Server, version 20H1: KB5010793
• Windows 10, version 1909, Windows Server, version 1909: KB5010792
• Windows 10, version 1607, Windows Server 2016: KB5010790
• Windows 10, version 1507: KB5010789
• Windows 7 SP1: KB5010798
• Windows Server 2008 SP2: KB5010799

Updates for the following Windows versions are available only on Microsoft Update Catalog. For instructions, see the KB for your OS listed below:

• Windows 8.1, Windows Server 2012 R2: KB5010794
• Windows Server 2012: KB5010797

Microsoft release out-of-band fix for Windows 10 “Can’t connect to VPN. The L2TP connection attempt failed” error