A very small number of old browsers consider content as HTML
even when it is explicitly stated in the Content-Type header
that it is not. If content served is based on user-supplied
input, then an XSS is possible. Introduce three mitigations:
+ Don't reflect user input in error strings
+ Set a Content-Disposition header when requesting a resource
that should never be displayed in a browser window
+ Set X-Content-Type-Options: nosniff on all responses