CVE-2025-4392 is a high-severity Stored Cross-Site Scripting (XSS) vulnerability affecting the WordPress plugin 'Shared Files – Frontend File Upload Form & Secure File Sharing' developed by anssilaitila. This vulnerability exists in all versions up to and including 1.7.48. The root cause is insufficient input sanitization and output escaping in the sanitize_file() function, which is responsible for validating uploaded files. Specifically, the plugin attempts to restrict uploads by MIME type but fails to properly neutralize malicious HTML content embedded within uploaded .html files. As a result, unauthenticated attackers can bypass MIME-type checks and upload crafted HTML files containing arbitrary JavaScript code. When any user subsequently accesses these malicious HTML files through the plugin's interface, the embedded scripts execute in the context of the victim's browser. This leads to the compromise of confidentiality and integrity of user data, session hijacking, or further exploitation within the affected WordPress site. The vulnerability requires no authentication or user interaction to exploit, and the attack surface is broad since the plugin is publicly accessible on many WordPress sites. The CVSS v3.1 base score is 7.2 (high), reflecting network attack vector, low attack complexity, no privileges required, no user interaction, and a scope change due to impact extending beyond the vulnerable component. Although no known exploits are currently reported in the wild, the vulnerability's nature and ease of exploitation make it a significant threat to WordPress sites using this plugin.

For European organizations using WordPress sites with the vulnerable Shared Files plugin, this vulnerability poses a serious risk. Attackers can inject persistent malicious scripts that execute in the browsers of site visitors or internal users, potentially leading to credential theft, session hijacking, unauthorized actions, or distribution of malware. This can result in data breaches, loss of customer trust, regulatory non-compliance (e.g., GDPR violations due to personal data exposure), and reputational damage. Organizations relying on this plugin for secure file sharing may inadvertently expose sensitive documents or enable lateral movement within their networks. Given the plugin's role in frontend file uploads, the attack vector is exposed to external threat actors without authentication, increasing the likelihood of exploitation. The scope of impact extends beyond the compromised plugin to the entire WordPress site and its users, amplifying potential damage. European entities in sectors such as finance, healthcare, government, and critical infrastructure, which often use WordPress for public-facing portals, are particularly at risk due to the sensitivity of their data and regulatory scrutiny.

1. Immediate update or patch: Organizations should check for and apply any official patches or updates from the plugin vendor addressing CVE-2025-4392. If no patch is available, consider disabling or uninstalling the plugin until a fix is released. 2. Implement strict file upload controls: Restrict allowed file types to safe formats and enforce server-side validation beyond MIME type checks, including content inspection to detect embedded scripts. 3. Use Web Application Firewalls (WAFs): Deploy WAF rules that detect and block malicious payloads targeting XSS vulnerabilities, especially those involving HTML file uploads. 4. Harden WordPress security: Limit plugin usage to trusted and actively maintained plugins, enforce least privilege principles for user roles, and regularly audit installed plugins for vulnerabilities. 5. Content Security Policy (CSP): Implement CSP headers to restrict the execution of unauthorized scripts in browsers, mitigating the impact of stored XSS. 6. Monitor logs and user activity: Set up monitoring to detect unusual file uploads or access patterns that may indicate exploitation attempts. 7. Educate users and administrators: Raise awareness about the risks of file upload vulnerabilities and encourage prompt reporting of suspicious site behavior. These measures, combined, reduce the attack surface and limit the potential damage from exploitation of this vulnerability.