[valid_referers] none in valid_referers

Module ngx_http_referer_module allows to block the access to service for requests with wrong Referer value. It's often used for setting X-Frame-Options header (ClickJacking protection), but there may be other cases.

Typical problems with this module's config: * use of server_names with bad server name (server_name directive); * too broad and/or bad regexes; * use of none.

Notice: at the moment, Gixy can only detect the use of none as a valid referer.

Why none is bad?

According to docs:

none - the “Referer” field is missing in the request header;

Still, it's important to remember that any resource can make user's browser to make a request without a Referer request header. E.g.: - in case of redirect from HTTPS to HTTP; - by setting up the Referrer Policy; - a request with opaque origin, data: scheme, for example.

So, by using none as a valid referer, you nullify any attemps in refferer validation.