CVE-2025-56304 is a cross-site scripting (XSS) vulnerability identified in YzmCMS, a content management system, affecting versions up to 7.3. The vulnerability arises from improper sanitization of the HTTP Referer header on the user registration page. An attacker can craft a malicious Referer header containing executable JavaScript code, which, when processed by the vulnerable page, results in the script being executed in the context of the victim's browser. This type of reflected XSS attack requires user interaction, specifically the victim visiting the registration page with the malicious Referer header. The vulnerability has a CVSS 3.1 base score of 6.1, indicating a medium severity level. The vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N) shows that the attack can be performed remotely over the network without privileges, requires low attack complexity, no privileges, but does require user interaction. The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component. The impact affects confidentiality and integrity to a limited extent, with no impact on availability. No known exploits are reported in the wild, and no patches have been linked yet. The vulnerability is classified under CWE-79, which covers improper neutralization of input during web page generation leading to XSS.

For European organizations using YzmCMS, especially those running versions up to 7.3, this vulnerability poses a risk of client-side script injection during user registration. Successful exploitation could allow attackers to steal session cookies, perform actions on behalf of users, or redirect users to malicious sites, potentially leading to account compromise or data leakage. Although the impact on confidentiality and integrity is limited, the scope change indicates that the vulnerability could affect other components or user sessions beyond the registration page. This could undermine user trust and lead to reputational damage, especially for organizations handling sensitive user data or operating in regulated sectors such as finance, healthcare, or e-commerce. The requirement for user interaction limits the attack vector but does not eliminate risk, particularly if attackers can lure users to the registration page via phishing or social engineering. The absence of known exploits in the wild reduces immediate risk but does not preclude future exploitation. Given the medium severity, organizations should prioritize remediation to prevent potential exploitation.

European organizations should implement the following specific mitigations: 1) Immediately review and sanitize the Referer header input on the registration page, employing robust input validation and output encoding to neutralize any injected scripts. 2) Apply Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of XSS attacks. 3) Monitor web server and application logs for unusual Referer header values or suspicious registration page access patterns. 4) Educate users and administrators about phishing risks that could lead to exploitation of this vulnerability. 5) If possible, upgrade YzmCMS to a version where this vulnerability is patched once available. 6) Consider implementing Web Application Firewalls (WAFs) with rules specifically designed to detect and block malicious Referer headers or XSS payloads targeting the registration page. 7) Conduct regular security assessments and penetration tests focusing on input validation and XSS vulnerabilities in web applications.