Smoothwall Express 3.1-SP4-polar-x86_64-update9 contains multiple cross-site scripting vulnerabilities in the proxy.cgi endpoint that allow attackers to inject malicious scripts through parameters including CACHE_SIZE, MAX_SIZE, MIN_SIZE, MAX_OUTGOING_SIZE, and MAX_INCOMING_SIZE. Attackers can submit POST requests with script payloads to store or reflect arbitrary JavaScript code that executes in users' browsers when the proxy configuration page is accessed.