I have request filtering enabled and "Allow unlisted file name extensions" is set to false. When requesting any normal path, including "<http://localhost>" I get a 404.7 error - "The request filtering module is configured to deny the file extension." 

If I set "Allow unlisted file name extensions" to true then the site works fine.

I know that "<http://localhost/>" maps to Views/Homes/Index.cshtml" and .cshtml is explicitly allowed.

I am trying to figure out which file extension is causing the issue but can't find anything in the logs. I have all 55 "default" file types set to allow.