CVE-2025-13512 is a reflected cross-site scripting vulnerability identified in the CoSign Single Signon plugin for WordPress, developed by jiangxin. This vulnerability exists due to improper neutralization of input during web page generation, specifically involving the $_SERVER['PHP_SELF'] parameter. All versions up to and including 0.3.1 are affected. The plugin fails to adequately sanitize and escape this input, allowing unauthenticated attackers to craft URLs containing malicious JavaScript code. When a victim clicks such a URL, the injected script executes in their browser context, potentially leading to session hijacking, credential theft, or unauthorized actions performed with the victim's privileges. The vulnerability does not require authentication but does require user interaction (clicking a malicious link). The CVSS 3.1 base score is 6.1, reflecting medium severity with network attack vector, low attack complexity, no privileges required, user interaction required, and impacts on confidentiality and integrity but not availability. No public exploits are currently known. The vulnerability affects the confidentiality and integrity of user sessions and data but does not directly impact system availability. The reflected XSS nature means the attack surface is primarily public-facing web pages where the plugin is active. The vulnerability is particularly concerning for organizations that rely on CoSign Single Signon for authentication in WordPress environments, as it could facilitate phishing campaigns or session hijacking attacks. The lack of an official patch at the time of reporting means organizations must rely on interim mitigations such as input validation, output encoding, and web application firewall rules. Monitoring for suspicious URL parameters and educating users to avoid clicking untrusted links are also critical defense measures.

For European organizations, this vulnerability poses a moderate risk primarily to the confidentiality and integrity of user sessions and data. Attackers can exploit the vulnerability to steal session cookies, impersonate users, or conduct phishing attacks that leverage the trusted authentication mechanism provided by CoSign Single Signon. This could lead to unauthorized access to sensitive corporate resources, data leakage, or further lateral movement within networks. The impact is particularly significant for organizations with public-facing WordPress sites that use this plugin for single sign-on, including government portals, financial institutions, and enterprises with customer-facing applications. While availability is not directly affected, the reputational damage and potential regulatory consequences under GDPR for data breaches could be substantial. The requirement for user interaction limits the attack scope but does not eliminate risk, especially in environments where phishing is prevalent. The absence of known exploits in the wild provides a window for proactive mitigation, but the medium CVSS score indicates that the vulnerability should be addressed promptly to prevent exploitation.

1. Monitor for and apply any official patches or updates from jiangxin for the CoSign Single Signon plugin as soon as they become available. 2. Implement strict input validation and output encoding on the $_SERVER['PHP_SELF'] parameter within the plugin or via custom code to neutralize malicious scripts. 3. Deploy Web Application Firewalls (WAFs) with rules specifically designed to detect and block reflected XSS payloads targeting the affected parameter. 4. Conduct regular security audits and penetration testing focused on the WordPress environment and authentication plugins to identify similar injection points. 5. Educate end-users and administrators about the risks of clicking on suspicious links, especially those that may appear to originate from trusted internal sources. 6. Restrict the exposure of the CoSign Single Signon plugin pages to only necessary users or IP ranges where feasible to reduce attack surface. 7. Employ Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in browsers. 8. Monitor web server logs for unusual requests containing suspicious payloads in the PHP_SELF parameter to detect attempted exploitation. 9. Consider alternative authentication mechanisms or plugins with a stronger security track record if immediate patching is not possible.