Microsoft’s latest security patch has caused issues with local web setup, particularly with IIS (Internet Information Services) on Windows 11 systems. The KB5066835 update is affecting developers and system admins who rely on IIS for their work.
Symptoms include errors related to secure connections and disruptions in server connectivity. Even professional software like Autodesk Vault has been affected, slowing down daily work. Microsoft’s support staff have acknowledged the issue and provided guidance, including updating Microsoft Defender definitions and temporarily uninstalling KB5066835 and KB5065789.
Community-sourced workarounds are available, such as disabling HTTP/2 on the host by adding registry values under HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters. This is a temporary fix, but it can help resolve specific issues. If you’re affected, try updating Defender definitions first and testing the HTTP/2 toggle before considering uninstalling updates.
Source: https://piunikaweb.com/2025/10/16/windows-11-kb5066835-iis-localhost-fix