CVE-2025-62698 is a stored Cross-site Scripting (XSS) vulnerability classified under CWE-79, found in the ExternalGuidance extension of Mediawiki, a popular open-source wiki platform developed by The Wikimedia Foundation. The flaw stems from improper neutralization of user-supplied input during the generation of web pages, allowing malicious scripts to be injected and persist on pages served to other users. This vulnerability affects the master branch of Mediawiki ExternalGuidance prior to version 1.39. The CVSS 4.0 vector indicates that the attack can be performed remotely over the network (AV:N) with low attack complexity (AC:L), requiring no privileges (PR:N) or user interaction (UI:N). The impact on confidentiality, integrity, and availability is limited but non-negligible (VC:L, VI:L, VA:L), and the scope is limited (SC:L) with low impact on security requirements (SI:L, SA:L). Stored XSS can enable attackers to execute arbitrary JavaScript in the context of the victim’s browser, potentially leading to session hijacking, defacement, or redirection to malicious sites. Although no exploits are currently known in the wild, the vulnerability presents a credible risk, especially for organizations relying on Mediawiki for collaborative content management. The lack of authentication or user interaction requirements increases the ease of exploitation, making it important to address promptly. The Wikimedia Foundation has not yet released a patch, so users should monitor official channels for updates.

For European organizations, the impact of CVE-2025-62698 can be significant, particularly for public sector entities, educational institutions, and enterprises that use Mediawiki for internal knowledge bases or public documentation. Exploitation of this stored XSS vulnerability could allow attackers to execute malicious scripts in the browsers of users accessing affected Mediawiki pages, leading to theft of authentication tokens, unauthorized actions performed on behalf of users, or distribution of malware. This can compromise sensitive information, disrupt operations, and damage organizational reputation. Given Mediawiki’s widespread use in government and academia across Europe, the risk of targeted attacks exploiting this vulnerability is heightened. Additionally, organizations subject to stringent data protection regulations such as GDPR may face compliance risks if user data confidentiality is breached. The medium severity rating reflects a moderate but actionable threat that requires timely mitigation to prevent exploitation and potential lateral movement within networks.

1. Monitor official Wikimedia Foundation channels for the release of a security patch for Mediawiki ExternalGuidance and apply it immediately upon availability. 2. In the interim, disable or restrict the ExternalGuidance extension if feasible to reduce the attack surface. 3. Implement rigorous input validation and output encoding on all user-supplied data within Mediawiki pages, especially those rendered by ExternalGuidance. 4. Deploy Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS payloads. 5. Conduct regular security audits and code reviews focusing on input handling in custom Mediawiki extensions or templates. 6. Educate Mediawiki administrators and users about the risks of XSS and encourage vigilance for suspicious content or behavior. 7. Employ web application firewalls (WAFs) with rules designed to detect and block XSS attack patterns targeting Mediawiki. 8. Monitor logs and user reports for signs of exploitation attempts or anomalous script execution. 9. Consider isolating Mediawiki instances or restricting access to trusted networks to limit exposure. 10. Maintain up-to-date backups to enable rapid recovery in case of compromise.