CVE-2025-13839 is a stored cross-site scripting (XSS) vulnerability identified in the LJUsers plugin for WordPress, specifically affecting all versions up to and including 1.2.0. The vulnerability stems from improper neutralization of input during web page generation, classified under CWE-79. The flaw exists in the handling of the 'name' parameter within the 'ljuser' shortcode, where insufficient input sanitization and output escaping allow authenticated users with Contributor-level privileges or higher to inject arbitrary JavaScript code. This malicious code is stored persistently and executed in the browsers of any users who access the affected pages, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. The vulnerability has a CVSS 3.1 base score of 6.4, indicating medium severity. The attack vector is network-based (remote), requires low attack complexity, and privileges of a Contributor or above, but does not require user interaction. The scope is changed, meaning the vulnerability can affect resources beyond the initially compromised component, such as user sessions or other site data. No known exploits have been reported in the wild as of the publication date. The vulnerability highlights the risks of insufficient input validation in WordPress plugins, especially those that allow user-generated content or attributes to be rendered directly in pages. Since WordPress is widely used across Europe for blogs, corporate sites, and e-commerce, this vulnerability could be leveraged to compromise site integrity and user trust.

For European organizations, this vulnerability could lead to unauthorized script execution within the context of affected WordPress sites, compromising user confidentiality and data integrity. Attackers with Contributor-level access could inject scripts that steal session cookies, perform actions on behalf of other users, or redirect visitors to malicious sites. This could result in data breaches, reputational damage, and loss of customer trust. Organizations relying on WordPress for public-facing websites, intranets, or customer portals are particularly at risk. The impact is heightened in sectors with strict data protection regulations such as GDPR, where unauthorized data exposure can lead to legal penalties. Additionally, the persistent nature of stored XSS means that once exploited, the malicious code remains active until removed, increasing the window of exposure. Although availability is not directly impacted, the indirect effects on business operations and compliance can be significant.

European organizations should immediately review their use of the LJUsers plugin and upgrade to a patched version once available. In the absence of a patch, restrict Contributor-level permissions to trusted users only and consider temporarily disabling the plugin. Implement web application firewalls (WAFs) with rules to detect and block malicious scripts in shortcode parameters. Conduct thorough input validation and output encoding for all user-supplied data in custom shortcodes or plugins. Regularly audit WordPress user roles and permissions to minimize the number of users with elevated privileges. Monitor website logs and content for unusual shortcode usage or injected scripts. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts. Educate site administrators and content creators about the risks of XSS and safe content practices. Finally, maintain an incident response plan to quickly address any detected exploitation attempts.