CVE-2025-13899 identifies a stored Cross-Site Scripting (XSS) vulnerability in the TR Timthumb plugin for WordPress, maintained by pntrinh. This vulnerability affects all versions up to and including 1.0.4. The root cause is improper neutralization of input during web page generation, specifically insufficient sanitization and escaping of shortcode attributes. Authenticated users with Contributor-level access or higher can exploit this flaw by injecting arbitrary JavaScript code into shortcode attributes embedded in WordPress pages. When any user subsequently accesses these pages, the malicious scripts execute in their browsers, potentially compromising session tokens, redirecting users, or performing unauthorized actions within the context of the victim’s session. The vulnerability does not require user interaction beyond page access, and the attack scope is limited to sites using the vulnerable plugin. The CVSS 3.1 base score of 6.4 reflects a medium severity, with network attack vector, low attack complexity, requiring privileges but no user interaction, and partial impact on confidentiality and integrity. No patches or official fixes are currently linked, and no known exploits have been reported in the wild. The vulnerability is classified under CWE-79, a common web application security weakness related to Cross-Site Scripting. The plugin’s widespread use in WordPress sites makes this a relevant threat for web administrators and security teams.

For European organizations, this vulnerability poses a significant risk to the confidentiality and integrity of web applications running WordPress with the TR Timthumb plugin. Exploitation can lead to session hijacking, unauthorized actions performed on behalf of users, defacement, or distribution of malware through compromised pages. Organizations with Contributor-level users who can publish or edit content are particularly vulnerable, as these users can inject malicious scripts. This may result in reputational damage, data breaches involving user credentials or personal data, and potential regulatory non-compliance under GDPR if personal data is compromised. The medium severity indicates that while the vulnerability is exploitable remotely, it requires authenticated access, somewhat limiting the attack surface. However, given the popularity of WordPress in Europe and the common use of plugins for site customization, many organizations could be exposed. Attackers targeting media, e-commerce, or governmental websites could leverage this vulnerability for persistent attacks or lateral movement within networks.

1. Immediately update the TR Timthumb plugin to a version that addresses this vulnerability once available. If no patch exists, consider disabling or removing the plugin until a fix is released. 2. Restrict Contributor-level and higher privileges to trusted users only, minimizing the risk of malicious script injection. 3. Implement strict input validation and output encoding for all shortcode attributes and user-generated content to prevent script injection. 4. Employ Web Application Firewalls (WAFs) with rules to detect and block XSS payloads targeting shortcode parameters. 5. Conduct regular security audits and code reviews of WordPress plugins and themes to identify similar vulnerabilities. 6. Educate content contributors about safe content practices and the risks of injecting untrusted code. 7. Monitor web server logs and user activity for unusual behavior indicative of exploitation attempts. 8. Use Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts on web pages. These steps collectively reduce the likelihood and impact of exploitation beyond generic patching advice.