CVE-2025-13512 is a reflected Cross-Site Scripting (XSS) vulnerability identified in the jiangxin CoSign Single Signon plugin for WordPress, affecting all versions up to and including 0.3.1. The root cause is insufficient sanitization and escaping of the $_SERVER['PHP_SELF'] parameter during web page generation, which allows an attacker to inject arbitrary JavaScript code into pages served by the plugin. Because the vulnerability is reflected, the malicious script is embedded in a crafted URL that, when clicked by a victim, causes the script to execute in the victim’s browser context. This attack vector requires no authentication but does require user interaction (clicking a malicious link). The vulnerability impacts confidentiality and integrity by potentially enabling session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The CVSS 3.1 score is 6.1, reflecting medium severity with network attack vector, low attack complexity, no privileges required, and user interaction needed. No patches or exploits are currently known, but the vulnerability is publicly disclosed. The plugin is used in WordPress environments to provide single sign-on capabilities, making it a critical component for user authentication flows. Without proper input validation and output encoding, the plugin exposes users to XSS attacks that can undermine trust and security of affected websites.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of user sessions and data. Exploitation could lead to session hijacking, allowing attackers to impersonate legitimate users and access sensitive information or perform unauthorized actions. This is particularly concerning for organizations relying on the CoSign Single Signon plugin for authentication across multiple services. Although availability is not directly impacted, the reputational damage and potential regulatory consequences under GDPR for data breaches involving personal data could be significant. Organizations operating e-commerce, government portals, or critical infrastructure with WordPress-based authentication are at higher risk. The requirement for user interaction limits mass exploitation but targeted phishing campaigns could be effective. The lack of known exploits currently reduces immediate risk but patching and mitigation should be prioritized to prevent future attacks.

1. Immediately update or patch the CoSign Single Signon plugin once a fix is released by the vendor. 2. Until a patch is available, disable or remove the plugin if feasible to eliminate the attack surface. 3. Implement Web Application Firewall (WAF) rules to detect and block suspicious requests containing malicious payloads targeting the $_SERVER['PHP_SELF'] parameter. 4. Educate users and administrators about phishing risks and encourage caution when clicking unknown or suspicious links. 5. Employ Content Security Policy (CSP) headers to restrict execution of unauthorized scripts in browsers. 6. Conduct regular security assessments and code reviews of custom plugins and authentication mechanisms. 7. Monitor logs for unusual URL patterns or repeated attempts to exploit this vulnerability. 8. Use security plugins that provide XSS protection and input sanitization for WordPress environments. 9. Limit the scope of the plugin’s permissions and isolate authentication components where possible. 10. Prepare incident response plans to quickly address any exploitation attempts.