CVE-2025-13966 is a stored Cross-Site Scripting (XSS) vulnerability identified in the Paypal Payment Shortcode plugin for WordPress, specifically affecting all versions up to and including 1.01. The vulnerability stems from improper neutralization of input during web page generation, classified under CWE-79. The flaw exists in the handling of the 'buttom_image' parameter within the [paypal-shortcode] shortcode, where insufficient input sanitization and output escaping allow authenticated users with Contributor-level or higher privileges to inject arbitrary JavaScript code. Because the injected scripts are stored and rendered on pages accessed by other users, this can lead to persistent XSS attacks. The vulnerability's CVSS 3.1 score is 6.4, reflecting a medium severity with network attack vector, low attack complexity, requiring privileges but no user interaction, and impacting confidentiality and integrity with a scope change. Exploitation could enable attackers to steal session cookies, perform actions on behalf of other users, or deliver further payloads. No patches or fixes have been officially released as of the publication date, and no known exploits are reported in the wild. The vulnerability is particularly concerning for WordPress sites with multiple contributors where malicious users could leverage this to escalate attacks against site visitors or administrators.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on WordPress websites with the Paypal Payment Shortcode plugin installed. Exploitation could lead to unauthorized disclosure of sensitive user information, session hijacking, and potential defacement or manipulation of website content, damaging brand reputation and user trust. E-commerce sites using this plugin for payment processing could face financial fraud risks or customer data compromise. Since the vulnerability requires authenticated Contributor-level access, insider threats or compromised contributor accounts pose a realistic attack vector. The persistent nature of the XSS increases risk as malicious scripts remain active until removed. Given the widespread use of WordPress across Europe and the popularity of PayPal payment integrations, organizations in sectors such as retail, finance, and public services are particularly vulnerable. Regulatory compliance risks also arise under GDPR if personal data is exposed or mishandled due to exploitation.

Immediate mitigation steps include restricting Contributor-level access to trusted users only and auditing existing contributor accounts for suspicious activity. Website administrators should disable or remove the Paypal Payment Shortcode plugin until a security patch is released. If removal is not feasible, implement Web Application Firewall (WAF) rules to detect and block malicious payloads targeting the 'buttom_image' parameter. Employ Content Security Policy (CSP) headers to limit the execution of unauthorized scripts on affected pages. Regularly scan the website for injected scripts and sanitize existing content to remove malicious code. Monitor logs for unusual activity related to shortcode usage. Educate contributors on secure input practices and the risks of injecting untrusted content. Finally, maintain up-to-date backups to enable quick restoration if compromise occurs. Once a patch is available, apply it promptly to fully remediate the vulnerability.