CVE-2025-13839 identifies a stored Cross-Site Scripting vulnerability in the LJUsers plugin for WordPress, specifically affecting all versions up to and including 1.2.0. The vulnerability stems from insufficient sanitization and escaping of user-supplied input in the 'name' parameter of the 'ljuser' shortcode. This flaw allows authenticated users with Contributor-level or higher privileges to inject arbitrary JavaScript code into pages. When other users access these pages, the injected scripts execute in their browsers, potentially leading to session hijacking, privilege escalation, or unauthorized actions within the context of the affected website. The vulnerability is classified under CWE-79, which covers improper neutralization of input during web page generation. The CVSS v3.1 score of 6.4 reflects a medium severity, with an attack vector of network, low attack complexity, requiring privileges (PR:L), no user interaction (UI:N), and a scope change (S:C). The impact affects confidentiality and integrity but not availability. No known exploits are publicly available yet, but the vulnerability's presence in a popular CMS plugin makes it a notable risk. The issue highlights the importance of proper input validation and output encoding in web applications, especially those allowing user-generated content. Since the vulnerability requires authenticated access, it is less likely to be exploited by anonymous attackers but remains a significant threat in environments where Contributor-level access is granted to untrusted users. The lack of a patch link suggests that remediation may require manual code review or updates from the vendor. Organizations relying on LJUsers should assess their exposure and implement compensating controls promptly.

For European organizations, this vulnerability poses a risk primarily to websites running WordPress with the LJUsers plugin installed, especially if Contributor-level or higher user roles are assigned to untrusted individuals. Exploitation can lead to theft of session cookies, unauthorized actions performed on behalf of other users, and potential compromise of user data confidentiality and integrity. While availability is not impacted, the reputational damage and potential regulatory consequences under GDPR for data breaches involving user information could be significant. Organizations with public-facing WordPress sites that allow user-generated content or community contributions are particularly vulnerable. Attackers could leverage this vulnerability to escalate privileges or conduct phishing attacks by injecting malicious scripts. The medium severity score indicates a moderate but actionable threat, emphasizing the need for timely mitigation. The absence of known exploits in the wild reduces immediate risk but does not preclude future exploitation. European entities with strict compliance requirements should prioritize addressing this vulnerability to avoid legal and operational repercussions.

1. Immediately review and restrict Contributor-level and higher user roles to trusted personnel only, minimizing the risk of malicious script injection. 2. Implement strict input validation and output encoding for all user-supplied data, particularly the 'name' parameter in the 'ljuser' shortcode, to neutralize potentially harmful scripts. 3. Monitor WordPress sites for unusual shortcode usage or unexpected script injections using web application firewalls (WAF) and security plugins. 4. Apply principle of least privilege on user roles and consider disabling or removing the LJUsers plugin if it is not essential. 5. Conduct regular security audits and code reviews of custom plugins or themes that interact with user input. 6. Stay updated with vendor announcements for patches or updates addressing this vulnerability and apply them promptly once available. 7. Educate site administrators and content contributors about the risks of XSS and safe content practices. 8. Use Content Security Policy (CSP) headers to limit the execution of unauthorized scripts on affected sites. 9. Employ multi-factor authentication (MFA) to reduce the risk of compromised user accounts being used to exploit this vulnerability. 10. Backup website data regularly to enable recovery in case of compromise.