The vulnerability identified as CVE-2025-13859 affects the AffiliateX – Amazon Affiliate Plugin for WordPress, specifically versions from 1.0.0 up to 1.3.9.3. The root cause is a missing authorization check (CWE-862) on the AJAX action save_customization_settings, which is responsible for saving customization settings within the plugin. This flaw allows any authenticated user with at least Subscriber-level privileges to bypass intended access controls and inject arbitrary JavaScript code into the plugin's customization settings. When the AffiliateX block is rendered on the WordPress site, the injected JavaScript executes in the context of the site, potentially leading to cross-site scripting (XSS) attacks. Such attacks can be leveraged to steal session cookies, perform actions on behalf of other users, or redirect visitors to malicious sites. The vulnerability does not require user interaction beyond the attacker being authenticated, and it does not impact system availability. The CVSS v3.1 score of 6.4 reflects a medium severity, considering the network attack vector, low attack complexity, and the need for low privileges but no user interaction. No patches are currently linked, and no known exploits have been reported in the wild, indicating that exploitation might require some attacker effort or knowledge. The vulnerability is particularly concerning for WordPress sites that allow user registration with Subscriber or higher roles, as attackers could exploit compromised or malicious user accounts to inject malicious scripts site-wide.

For European organizations, this vulnerability poses a risk to the confidentiality and integrity of WordPress sites using the AffiliateX plugin. Attackers can inject malicious JavaScript that may lead to session hijacking, data theft, or unauthorized actions performed under the guise of legitimate users. This can damage brand reputation, lead to data breaches involving customer information, and potentially result in regulatory non-compliance under GDPR if personal data is compromised. The impact is heightened for e-commerce and affiliate marketing sites that rely on AffiliateX for revenue generation, as malicious scripts could redirect customers or manipulate affiliate links. Although availability is not directly affected, the indirect consequences of trust erosion and potential blacklisting by search engines or security services could disrupt business operations. The requirement for authenticated access limits the attack surface but does not eliminate risk, especially in environments with weak user account management or where subscriber accounts are easily created or compromised.

European organizations should immediately audit their WordPress installations to identify the presence of the AffiliateX – Amazon Affiliate Plugin and verify the version in use. Until an official patch is released, administrators should restrict user registration and limit Subscriber-level access to trusted users only. Implementing Web Application Firewall (WAF) rules to detect and block suspicious AJAX requests targeting save_customization_settings can help mitigate exploitation attempts. Regularly review plugin settings and customization blocks for unauthorized JavaScript injections. Employ Content Security Policy (CSP) headers to restrict the execution of inline scripts and reduce the impact of injected JavaScript. Monitor logs for unusual activity related to AJAX calls and user behavior indicative of exploitation attempts. Plan to update the plugin promptly once a vendor patch becomes available. Additionally, consider disabling or removing the plugin if it is not essential to reduce the attack surface.