CVE-2025-53491 is a Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the FlaggedRevs extension of the Mediawiki software maintained by the Wikimedia Foundation. This vulnerability exists in versions 1.43.x prior to 1.43.2. The issue arises due to improper neutralization of user-supplied input during web page generation, allowing malicious actors to inject and execute arbitrary scripts in the context of the affected web application. The vulnerability requires network access (AV:N), low attack complexity (AC:L), and privileges (PR:L) with user interaction (UI:R) to exploit, and it impacts confidentiality and integrity with a scope change (S:C). The CVSS v3.1 base score is 5.4, indicating a medium severity level. Exploitation could allow attackers to steal session tokens, manipulate page content, or perform actions on behalf of authenticated users. No known exploits are currently reported in the wild, and no patches are linked yet, but the vulnerability is publicly disclosed and should be addressed promptly. The FlaggedRevs extension is used to manage content revisions and approvals in Mediawiki installations, which are widely deployed in collaborative knowledge bases and documentation platforms.

For European organizations, particularly those running Mediawiki with the FlaggedRevs extension, this vulnerability poses a risk to the confidentiality and integrity of their wiki content and user sessions. Attackers exploiting this XSS flaw could hijack user accounts, inject misleading or malicious content, and potentially disrupt collaborative workflows. This could lead to reputational damage, data leakage, and loss of trust among users and stakeholders. Public sector entities, educational institutions, and enterprises relying on Mediawiki for internal or public documentation are especially at risk. Given the collaborative nature of wikis, the impact could propagate through misinformation or unauthorized content changes. The medium severity score reflects that while the vulnerability requires some privileges and user interaction, the potential for scope change and data compromise is significant enough to warrant attention.

European organizations should immediately verify if their Mediawiki installations use the FlaggedRevs extension version 1.43.x prior to 1.43.2 and plan for an upgrade to the fixed version once available. In the interim, administrators should implement strict Content Security Policies (CSP) to restrict script execution and reduce XSS impact. Input validation and output encoding should be reviewed and enhanced in custom configurations or extensions interacting with FlaggedRevs. User privileges should be minimized to reduce the risk of exploitation, and user awareness training should emphasize caution with suspicious links or content. Monitoring web logs for unusual script injection attempts and employing web application firewalls (WAFs) with XSS detection rules can provide additional protection. Regular backups and integrity checks of wiki content can help detect and recover from unauthorized changes.