Microsoft is investigating major speed issues affecting L2TP/IPsec VPN connections after installing recent Windows 11 updates.
According to reports from Windows users and administrators, connection bandwidth issues were first caused by the option KB5025305 April 2023 non-security update.
Redmond has incorporated the same fixes and improvements provided in preview update KB5025305 into the mandatory release KB5026372 cumulative update released on Patch Tuesday this month, causing the connection issues experienced by more Windows users.
“No issues connecting to VPN, once you get in, speeds are extremely slow and RDP just times out. A quick web search confirms that KB5025305 is causing speed issues on L2TP/IPsec VPN,” an admin Windows share on Reddit.
“Our users are faced with this, with a weird quirk: a group of 5-6 users are able to get speeds down 100m and up 80m, but the vast majority get speeds below 1m and less than 1m,” another admin told BleepingComputer.
Other user reports reveal that this issue apparently only affects Wi-Fi connections, with wired connections unaffected by the speed drop.
“Microsoft is aware of the issue and is reviewing it,” a spokesperson told BleepingComputer on Monday after contacting them about the speed issues.
Temporary fix for Windows 11 VPN speed issues
Although there is no workaround on affected Windows 11 systems until Microsoft provides a fix, Windows administrators have reported that uninstalling the problematic updates will resolve the issue.
“To remove the LCU after installing the combined SSU and LCU package, use the DISM /Remove-Package command line option with the LCU package name as an argument. You can find the package name using this order : DISM /online /get-packages“, Microsoft said.
However, it is important to note that Redmond is bundling all security fixes into a single update and therefore removing cumulative update KB5026372 will also remove all fixes for recently fixed security vulnerabilities, even though it can also fix VPN speed issues.
In mid-January 2022, Microsoft released emergency out-of-band (OOB) updates for troubleshoot L2TP VPN issues when trying to connect using the Windows VPN client, caused by January 2022 Patch Tuesday Updates.