CVE-2025-53500 is a security vulnerability classified under CWE-79, which pertains to Improper Neutralization of Input During Web Page Generation, commonly known as Cross-site Scripting (XSS). This vulnerability affects the MassEditRegex extension of the Mediawiki software developed by the Wikimedia Foundation. Specifically, versions 1.39.x (before 1.39.12), 1.42.x (before 1.42.7), and 1.43.x (before 1.43.2) are impacted. The flaw allows an attacker to inject malicious scripts that are stored persistently within the Mediawiki platform through the MassEditRegex extension. When other users access the affected pages, the malicious script executes in their browsers, potentially leading to session hijacking, unauthorized actions on behalf of users, theft of sensitive information, or distribution of malware. The vulnerability arises because the extension does not properly sanitize or neutralize user input during web page generation, allowing unsafe content to be embedded and rendered. Although no known exploits have been reported in the wild as of the publication date, the presence of stored XSS in a widely used wiki platform poses a significant risk, especially given Mediawiki's extensive deployment in public and private knowledge bases, including government, educational, and corporate environments. The lack of an assigned CVSS score indicates that the vulnerability is newly disclosed and may not yet have undergone full severity assessment, but the technical nature of stored XSS typically implies a high risk if exploited.

For European organizations, the impact of this vulnerability can be substantial. Mediawiki is widely used across Europe in various sectors such as government agencies, educational institutions, research organizations, and enterprises for collaborative documentation and knowledge management. Exploitation of this stored XSS vulnerability could lead to unauthorized access to sensitive internal information, compromise of user credentials, and potential lateral movement within networks. In government contexts, this could result in exposure of confidential policy documents or citizen data, undermining trust and compliance with regulations such as GDPR. For enterprises, the risk includes intellectual property theft and disruption of internal communications. Additionally, the persistent nature of stored XSS means that even trusted users can be targeted unknowingly, increasing the attack surface. The absence of known exploits currently provides a window for proactive mitigation, but the vulnerability's presence in multiple recent versions suggests a broad exposure. The impact on availability is generally low, but the confidentiality and integrity of data and user sessions are at significant risk.

To mitigate this vulnerability, organizations should prioritize updating the Mediawiki MassEditRegex extension to the fixed versions: 1.39.12, 1.42.7, or 1.43.2, depending on their installed version. If immediate patching is not feasible, administrators should consider disabling the MassEditRegex extension temporarily to prevent exploitation. Additionally, implementing strict Content Security Policy (CSP) headers can help reduce the risk of script execution from injected content. Regular auditing of wiki pages for suspicious or unexpected content, especially those modified via MassEditRegex, is recommended. Organizations should also enforce strict user access controls and monitor logs for unusual editing activities. Training users to recognize potential phishing or social engineering attempts that might leverage this vulnerability can further reduce risk. Finally, integrating web application firewalls (WAFs) with rules targeting XSS payloads may provide an additional layer of defense until patches are applied.