CVE-2025-62695 is a stored Cross-site Scripting (XSS) vulnerability classified under CWE-79, found in the WikiLambda Extension of the Mediawiki platform maintained by the Wikimedia Foundation. The vulnerability stems from improper neutralization of user-supplied input during the generation of web pages, allowing malicious scripts to be stored persistently within the wiki content. When other users access the affected pages, the embedded scripts execute in their browsers, potentially compromising their session cookies, redirecting them to malicious sites, or performing unauthorized actions on their behalf. This vulnerability affects the master branch of the WikiLambda Extension, which is used to extend Mediawiki's functionality with lambda calculus-based programming features. The CVSS 4.0 vector indicates that the attack can be performed remotely over the network without any authentication or user interaction, and it impacts confidentiality, integrity, and availability to a limited extent. Although no public exploits have been reported yet, the presence of stored XSS in a widely used platform like Mediawiki poses a significant risk, especially for organizations relying on collaborative knowledge bases. The vulnerability was published on October 21, 2025, and no official patches have been linked yet, highlighting the need for proactive mitigation. The Wikimedia Foundation is the vendor responsible for addressing this issue.

For European organizations, the impact of CVE-2025-62695 can be significant, particularly for those using Mediawiki with the WikiLambda Extension for internal or public knowledge management. Stored XSS can lead to session hijacking, enabling attackers to impersonate legitimate users and escalate privileges. It can also facilitate phishing attacks by injecting deceptive content or redirecting users to malicious websites. In environments where Mediawiki is used for critical documentation or collaborative development, data integrity may be compromised, and trust in the platform could be eroded. Public-facing wikis operated by government agencies, educational institutions, and NGOs are especially vulnerable to reputational damage and potential data breaches. The ease of exploitation without authentication increases the risk of widespread attacks, potentially affecting a large user base. Although the vulnerability has a medium severity rating, the broad deployment of Mediawiki in Europe amplifies its potential impact.

To mitigate CVE-2025-62695 effectively, European organizations should: 1) Monitor the Wikimedia Foundation's official channels for patches or updates to the WikiLambda Extension and apply them promptly once available. 2) Implement strict input validation and output encoding on all user-generated content within Mediawiki to prevent malicious scripts from being stored or rendered. 3) Deploy Content Security Policies (CSP) to restrict the execution of unauthorized scripts in users' browsers, thereby reducing the impact of any injected code. 4) Conduct regular security audits and code reviews of custom Mediawiki extensions to identify and remediate similar vulnerabilities. 5) Educate wiki administrators and users about the risks of XSS and encourage reporting of suspicious content. 6) Consider isolating or sandboxing the WikiLambda Extension if feasible, to limit the scope of potential exploitation. 7) Use web application firewalls (WAFs) configured to detect and block XSS attack patterns targeting Mediawiki installations. These measures, combined, will reduce the likelihood and impact of exploitation.