September 28, 2023

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New Windows KB5009543, KB5009566 updates crack L2TP VPN connections

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Windows 10 customers and directors report troubles earning L2TP VPN connections after installing the modern Home windows 10 KB5009543 and Home windows 11 KB5009566 cumulative updates.

Yesterday, Microsoft introduced Windows updates to take care of stability vulnerabilities and bugs as component of the January 2022 Patch Tuesday.

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

Updates break L2TP connections

Just after setting up yesterday’s updates, Windows users obtain their L2TP VPN connections broken when trying to link utilizing the Home windows VPN consumer.

When attempting to link to a VPN machine, they are demonstrated an mistake stating, “Won’t be able to connect to VPN. The L2TP connection endeavor failed due to the fact the stability layer encountered a processing mistake in the course of preliminary negotiations with the distant computer system,” as proven beneath.

Windows error when connecting to an LT2P VPN
Home windows error when connecting to an LT2P VPN

The Party Log will also log entries with error code 789, stating that the connection to the VPN failed.

Windows event log for failed L2TP VPN connection
Home windows party log for unsuccessful L2TP VPN connection

The bug is not affecting all VPN equipment and looks only to be affecting end users making use of the developed-in Home windows VPN consumer to make the connection.

A protection researcher acknowledged as Ronny on Twitter advised BleepingComputer that the bug affects their Ubiquiti Consumer-to-Internet site VPN connections for all those working with the Home windows VPN shopper.

Many Home windows admins also report on Reddit that the bug also influences connections to SonicWall, Cisco Meraki, and WatchGuard Firewalls, with the latter’s shopper also influenced by the bug.

With numerous end users nevertheless doing work remotely, admins have been pressured to clear away the KB5009566 and KB5009543 updates, which straight away fixes the L2TP VPN connections on reboot.

Home windows people can get rid of the KB5009566 and KB5009543 updates making use of the following instructions from an Elevated Command Prompt.

Home windows 10: wusa /uninstall /kb:5009543
Home windows 11: wusa /uninstall /kb:5009566

Even so, as Microsoft bundles all security updates in a single Home windows cumulative update, taking away the update will take out all fixes for vulnerabilities patched throughout the January Patch Tuesday. 

For that reason, Home windows admins want to weigh the challenges of unpatched vulnerabilities compared to the disruption caused by the inability to hook up to VPN connections.

It is not clear what brought about the bug, but Microsoft’s January Patch Tuesday fixed many vulnerabilities in the Home windows Net Critical Trade (IKE) protocol (CVE-2022-21843CVE-2022-21890CVE-2022-21883CVE-2022-21889CVE-2022-21848, and CVE-2022-21849) and in the Home windows Distant Obtain Connection Supervisor (CVE-2022-21914 and CVE-2022-21885) that could be leading to the problems.

Microsoft confirms bug, provides mitigation

Microsoft verified on Thursday that “Selected IPSEC connections may possibly fail” and that they will repair the concern in an upcoming release of Windows.

“Soon after installing KB5009543, IP Protection (IPSEC) connections which have a Seller ID could are unsuccessful. VPN connections making use of Layer 2 Tunneling Protocol (L2TP) or IP stability Online Crucial Exchange (IPSEC IKE) could possibly also be affected.”

Microsoft states that it may possibly be achievable to mitigate the bug by disabling the ‘Vendor ID,’ if feasible, on the VPN server.

“To mitigate the concern for some VPNs, you can disable Vendor ID inside the server-aspect configurations. Take note: Not all VPN servers have the selection to disable Seller ID from remaining applied,” Microsoft points out in a new acknowledged update difficulty.

Update 1/13/22: Extra update with extra facts from Microsoft.

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