zend-diactoros (and, by extension, Expressive), zend-http (and, by extension, Zend Framework MVC projects), and zend-feed (specifically, its PubSubHubbub sub-component) each contain a potential URL rewrite exploit. In each case, marshaling a request URI includes logic that introspects HTTP request headers that are specific to a given server-side URL rewrite mechanism. When these headers are present on systems not running the specific URL rewriting mechanism, the logic would still trigger, allowing a malicious client or proxy to emulate the headers to request arbitrary content.