CVE-2025-13966 identifies a stored Cross-Site Scripting (XSS) vulnerability in the Paypal Payment Shortcode plugin for WordPress, specifically affecting all versions up to and including 1.01. The vulnerability is due to improper neutralization of input during web page generation (CWE-79), where the 'buttom_image' parameter of the [paypal-shortcode] shortcode is insufficiently sanitized and escaped before rendering. This flaw allows authenticated attackers with Contributor-level privileges or higher to inject arbitrary JavaScript code into WordPress pages. Because the malicious script is stored in the page content, it executes whenever any user accesses the compromised page, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. The CVSS 3.1 base score is 6.4, reflecting network attack vector, low attack complexity, privileges required (low), no user interaction, and a scope change due to the impact extending beyond the vulnerable component. The vulnerability affects confidentiality and integrity but not availability. No patches or known exploits have been reported at the time of publication. The plugin is used to embed PayPal payment buttons via shortcode, making it a common feature on e-commerce or donation sites running WordPress. The flaw arises from a failure to properly sanitize the 'buttom_image' parameter, which is likely intended to specify an image URL or identifier but can be manipulated to include script code. This vulnerability underscores the importance of rigorous input validation and output encoding in WordPress plugins, especially those handling user-generated content or shortcode parameters.

For European organizations, this vulnerability could lead to significant risks if exploited. Attackers with Contributor-level access—often users who can create and edit content but not publish—can inject malicious scripts that execute in the browsers of site visitors or administrators. This can result in session hijacking, theft of sensitive information, unauthorized actions on the site, or distribution of malware. E-commerce and financial transaction sites using the Paypal Payment Shortcode plugin are particularly at risk, as attackers could manipulate payment flows or steal payment credentials indirectly. The confidentiality and integrity of user data and site content are at risk, potentially damaging organizational reputation and customer trust. Additionally, regulatory compliance under GDPR requires protection of personal data, and exploitation of this vulnerability could lead to data breaches with legal and financial consequences. The vulnerability does not affect availability directly but could be leveraged as part of broader attacks. Given WordPress’s widespread use across Europe, especially in small and medium enterprises, the exposure is non-trivial.

1. Immediate mitigation involves restricting Contributor-level user permissions to trusted individuals only, minimizing the risk of malicious content injection. 2. Disable or remove the Paypal Payment Shortcode plugin if it is not essential to business operations. 3. Implement Web Application Firewall (WAF) rules that detect and block suspicious script injections in shortcode parameters, particularly targeting the 'buttom_image' parameter. 4. Monitor and audit content created by Contributors for unexpected or suspicious code snippets. 5. Encourage plugin developers or site administrators to apply patches or updates once available; in the absence of official patches, consider custom code fixes that sanitize and escape the 'buttom_image' parameter properly before rendering. 6. Employ Content Security Policy (CSP) headers to restrict the execution of inline scripts and reduce the impact of XSS attacks. 7. Educate content creators on secure content practices and the risks of injecting untrusted data. 8. Regularly backup WordPress sites to enable recovery in case of compromise. These steps go beyond generic advice by focusing on access control, proactive monitoring, and layered defenses specific to the plugin’s functionality and the nature of the vulnerability.