CVE-2026-0671 is a security vulnerability classified under CWE-79, indicating improper neutralization of input during web page generation, commonly known as Cross-Site Scripting (XSS). This vulnerability specifically affects the UploadWizard extension of the MediaWiki platform, versions 1.39, 1.43, 1.44, and 1.45. The UploadWizard extension facilitates file uploads within MediaWiki, a widely used open-source wiki software. The flaw allows an attacker to inject malicious scripts into web pages generated by the UploadWizard, which can then be executed in the browsers of users who view the affected pages. This type of XSS can lead to session hijacking, theft of cookies or credentials, defacement, or redirection to malicious sites. The vulnerability stems from insufficient sanitization or encoding of user-supplied input before it is included in the HTML output. Although no public exploits have been reported yet, the vulnerability is publicly disclosed and thus could be targeted by attackers. The lack of a CVSS score indicates that the severity assessment must consider the potential impact and ease of exploitation. Since the vulnerability does not require authentication and can be triggered through user interaction (e.g., visiting a crafted page or uploading a malicious file), it poses a significant risk. MediaWiki is widely deployed by governments, educational institutions, and organizations across Europe, making this vulnerability relevant to a broad range of users.

For European organizations, this XSS vulnerability can lead to significant security risks including unauthorized access to user sessions, data leakage, and potential compromise of internal wiki content. Public sector entities and educational institutions that rely on MediaWiki for collaborative knowledge management are particularly vulnerable, as attackers could exploit the vulnerability to spread misinformation, deface content, or harvest credentials. The impact extends to loss of trust, reputational damage, and potential regulatory consequences under GDPR if personal data is compromised. Since MediaWiki is often used in multilingual and multi-user environments, the scope of impact can be broad, affecting many users simultaneously. Additionally, attackers could leverage this vulnerability as a foothold for further attacks within an organization’s network. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as the vulnerability is publicly known.

European organizations should prioritize upgrading the UploadWizard extension to a patched version once released by the Wikimedia Foundation. Until a patch is available, organizations should implement strict input validation and output encoding on all user-supplied data within the UploadWizard extension to prevent script injection. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. Regularly audit and monitor MediaWiki installations for unusual activity or attempted exploitation. Restrict upload permissions to trusted users and consider disabling the UploadWizard extension temporarily if feasible. Educate users about the risks of clicking on suspicious links or uploading untrusted content. Additionally, ensure that all MediaWiki instances are running the latest stable versions and that web application firewalls (WAFs) are configured to detect and block XSS attack patterns. Continuous vulnerability scanning and penetration testing focused on web application security will help identify residual risks.