CVE-2026-0671 is a Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the UploadWizard extension of the Wikimedia Foundation's MediaWiki software. The vulnerability exists due to improper neutralization of user-supplied input during the generation of web pages, which allows an attacker to inject malicious JavaScript code. The affected versions include 1.39, 1.43, 1.44, and 1.45 of the UploadWizard extension. The vulnerability can be exploited remotely without requiring authentication, but it requires user interaction, such as clicking a crafted link or uploading malicious content that triggers the script execution. The CVSS v3.1 base score is 6.1, indicating medium severity, with attack vector Network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:R), scope changed (S:C), and impacts on confidentiality and integrity (C:L/I:L) but no impact on availability (A:N). This vulnerability could allow attackers to steal session tokens, perform actions on behalf of users, or manipulate displayed content, potentially compromising user trust and data integrity. No patches or exploits are currently publicly available, but the issue is published and should be addressed promptly. The vulnerability is particularly relevant for organizations running MediaWiki with the UploadWizard extension, commonly used for collaborative content management and documentation.

For European organizations, the impact of CVE-2026-0671 can be significant, especially for public institutions, educational entities, and enterprises relying on MediaWiki for knowledge management and collaboration. Successful exploitation could lead to theft of user credentials or session cookies, enabling attackers to impersonate users and potentially escalate privileges. This undermines confidentiality and integrity of sensitive information stored or managed via MediaWiki platforms. Although availability is not directly affected, the reputational damage and potential data breaches could have regulatory consequences under GDPR, including fines and mandatory breach notifications. The requirement for user interaction limits automated exploitation but targeted phishing or social engineering campaigns could increase risk. The vulnerability also poses a risk to the integrity of content, as attackers might inject misleading or malicious information, affecting decision-making processes. Given the widespread use of MediaWiki in European public sectors and academia, the threat could disrupt critical knowledge-sharing infrastructures.

European organizations should implement the following specific mitigations: 1) Monitor for and apply updates to the UploadWizard extension as soon as patches become available from the Wikimedia Foundation. 2) In the interim, restrict or disable the UploadWizard extension if feasible, especially in high-risk environments. 3) Implement robust input validation and output encoding on all user-generated content within MediaWiki to prevent script injection. 4) Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts. 5) Educate users about the risks of clicking suspicious links or uploading untrusted content to reduce the likelihood of user interaction exploitation. 6) Conduct regular security audits and penetration testing focused on web application vulnerabilities, including XSS. 7) Monitor logs for unusual activity that could indicate exploitation attempts. 8) Consider deploying web application firewalls (WAFs) with rules tailored to detect and block XSS payloads targeting MediaWiki. These steps go beyond generic advice by focusing on immediate risk reduction and layered defenses specific to the MediaWiki UploadWizard context.