January-2022 Windows Updates

On January 11th, Microsoft released Windows updates to fix security vulnerabilities and bugs as part of the January 2022 Patch.

These updates include KB5009566 for Windows 11 and KB5009543 for Windows 10 2004, 20H1, and 21H1.

Windows 10 users and administrators report problems making L2TP VPN connections after installing the recent Windows 10 KB5009543 and Windows 11 KB5009566 cumulative updates.

Updates breaking L2TP connections

Microsoft confirms bug, provides mitigation

Microsoft confirmed on Thursday that "Certain IPSEC connections might fail" and that they will fix the issue in an upcoming release of Windows.

"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."

Microsoft states that it may be possible to mitigate the bug by disabling the 'Vendor ID,' if possible, on the VPN server.

"To mitigate the issue for some VPNs, you can disable Vendor ID within the server-side settings. Note: Not all VPN servers have the option to disable Vendor ID from being used," Microsoft explains in a new known update issue.

Windows users can remove the KB5009566 and KB5009543 updates using the following commands from an Elevated Command Prompt.

 Windows 10: wusa /uninstall /kb:5009543
 Windows 11: wusa /uninstall /kb:5009566

Uninstall Windows KB5009543 & KB5009566 updates

Here are the steps to uninstall the patch KB5009566 (for Windows 11) or KB5009543 (on Windows 10).

• Go to Control Panel --> Programs --> Programs and Features --> Installed Updates
• Depending on your OS click the patch KB5009566 (for Windows 11) or KB5009543 (on Windows 10) -->
• Click Uninstall
• Once the uninstallation is completed, reboot your machine and try connecting to VPN.

References

1. bleepingcomputer - New Windows KB5009543, KB5009566 updates break L2TP VPN connections