Silverstripe X-Forwarded-Host request hostname injection

Summary

A potential hostname injection vulnerability has been found which could allow attackers to alter url resolution. If a request contains the X-Forwarded-Host HTTP header a website would then use its value in place of the actual HTTP hostname. In cases where caching is enabled, this could allow an attacker to potentially embed a remote url as the base_url for any site. This would then cause other visitors to the site to be redirected unknowingly. This header is necessary for servers running behind a reverse proxy (such as nginx). Such servers are likely not vulnerable to this risk. A fix has been merged into the default installer, although existing projects which do not run behind a reverse proxy should update their htaccess as below: ``` <IfModule mod_headers.c> # Remove X-Forwarded-Host header sent as a part of any request from the web RequestHeader unset X-Forwarded-Host </IfModule> ```