In PHP versions 8.1.* before 8.1.31, 8.2.* before 8.2.26, 8.3.* before 8.3.14, when using streams with configured proxy and "request_fulluri" option, the URI is not properly sanitized which can lead to HTTP request smuggling and allow the attacker to use the proxy to perform arbitrary HTTP requests originating from the server, thus potentially gaining access to resources not normally available to the external user.