A reflected cross-site scripting (XSS) vulnerability exists in user/login.php at line 24 in ZZCMS 2023 and earlier. The application directly inserts the value of the HTTP_REFERER header into the HTML response without proper sanitization. An attacker can exploit this vulnerability by tricking a user into visiting a specially crafted URL, which includes a malicious Referer header. This can lead to the execution of arbitrary JavaScript code in the context of the victim's browser, potentially resulting in session hijacking, defacement, or other malicious activities.