SilverStripe Web Cache Poisoning through HTTPRequestBuilder

Silverstripe CMS sites through 4.4.4 which have opted into HTTP Cache Headers on responses served by the framework's HTTP layer can be vulnerable to web cache poisoning. Through modifying the X-Original-Url and X-HTTP-Method-Override headers, responses with malicious HTTP headers can return unexpected responses to other consumers of this cached response. Most other headers associated with web cache poisoning are already disabled through request hostname forgery whitelists.