CVE-2025-62663 is a stored Cross-Site Scripting (XSS) vulnerability identified in the UploadWizard extension of Mediawiki, an open-source wiki platform widely used for collaborative content management. The vulnerability is classified under CWE-79, which involves improper neutralization of input during web page generation. Specifically, the UploadWizard extension fails to adequately sanitize user-supplied input before rendering it on web pages, allowing attackers to inject malicious JavaScript code that is stored persistently. This stored XSS can be triggered when other users view the affected pages, enabling attackers to execute arbitrary scripts in the context of the victim's browser. The vulnerability affects the master branch of the UploadWizard extension prior to version 1.39. The CVSS 4.0 score of 6.9 reflects a medium severity, with an attack vector of network (remote exploitation), low attack complexity, no privileges or user interaction required, and limited impact on confidentiality, integrity, and availability. Although no public exploits have been reported, the vulnerability poses a risk of session hijacking, credential theft, defacement, or malware distribution. The Wikimedia Foundation has published the vulnerability details but has not yet released a patch, emphasizing the need for immediate mitigation steps by users. This vulnerability is particularly relevant for organizations that deploy Mediawiki for internal or public-facing knowledge bases, especially where the UploadWizard extension is enabled for file uploads and management.

For European organizations, the impact of CVE-2025-62663 can be significant, especially for those relying on Mediawiki for documentation, knowledge sharing, or public information portals. Exploitation of this stored XSS vulnerability could allow attackers to execute malicious scripts in the browsers of users accessing the affected Mediawiki instances. This can lead to unauthorized access to user sessions, theft of sensitive information such as login credentials, and potential spread of malware. Public sector entities, educational institutions, and large enterprises using Mediawiki may face reputational damage, data breaches, and operational disruptions. Given the collaborative nature of Mediawiki, the risk of widespread impact is elevated if attackers inject scripts that propagate through shared content. Additionally, attackers could leverage this vulnerability to conduct phishing campaigns or deface content, undermining trust in the affected organizations. The medium severity rating suggests a moderate but tangible risk that requires timely attention to prevent exploitation.

To mitigate CVE-2025-62663 effectively, European organizations should: 1) Monitor the Wikimedia Foundation’s official channels for the release of a security patch for the UploadWizard extension and apply updates promptly once available. 2) In the interim, consider disabling the UploadWizard extension if feasible to eliminate the attack surface. 3) Implement strict input validation and output encoding on any user-generated content within Mediawiki to prevent injection of malicious scripts. 4) Deploy Content Security Policies (CSP) to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 5) Conduct regular security audits and penetration testing focused on web application vulnerabilities, including XSS. 6) Educate users and administrators about the risks of XSS and encourage vigilance for suspicious activity or unexpected behavior in Mediawiki instances. 7) Employ web application firewalls (WAFs) with rules designed to detect and block XSS payloads targeting Mediawiki. 8) Review and limit user permissions to reduce the likelihood of malicious content being uploaded or edited by unauthorized users. These measures, combined with timely patching, will significantly reduce the risk posed by this vulnerability.