CVE-2025-62656 is a Stored Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the MediaWiki GlobalBlocking extension versions 1.43 and 1.44 maintained by The Wikimedia Foundation. The vulnerability stems from improper neutralization of user-supplied input during the generation of web pages, which allows attackers with high privileges to inject malicious scripts that are stored persistently within the application. When other users, potentially with lower privileges, view the affected pages, the malicious scripts execute in their browsers, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. The CVSS 4.0 vector indicates a network attack vector (AV:N) but requires high attack complexity (AC:H), no privileges required (PR:H), and user interaction (UI:P). The vulnerability impacts confidentiality primarily, with limited effects on integrity and availability. There are no known exploits in the wild yet, and no patches have been published at the time of disclosure. The GlobalBlocking extension is used to manage global blocks across Wikimedia projects, typically by administrators or trusted users, which means exploitation requires access to privileged accounts or insider threat scenarios. The vulnerability's presence in widely used versions 1.43 and 1.44 means that organizations running these versions are exposed until remediation is applied.

For European organizations, especially those in government, education, and public sectors that deploy MediaWiki with the GlobalBlocking extension, this vulnerability poses a risk of unauthorized script execution leading to data leakage or session compromise. Attackers exploiting this vulnerability could impersonate privileged users or steal sensitive information, undermining trust and confidentiality. Although the attack complexity is high and requires user interaction, the stored nature of the XSS means that once injected, multiple users can be affected. This could lead to widespread impact within organizations relying on MediaWiki for collaboration and knowledge management. The vulnerability could also be leveraged for phishing or social engineering campaigns targeting internal users. The lack of known exploits reduces immediate risk but does not eliminate the threat, especially given the strategic importance of MediaWiki in many European institutions.

Organizations should immediately audit their MediaWiki installations to identify if the GlobalBlocking extension versions 1.43 or 1.44 are in use. Until patches are released, restrict access to the GlobalBlocking extension to only the most trusted and trained administrators. Implement strict input validation and sanitization on all user inputs related to the extension, employing server-side filtering to neutralize potentially malicious scripts. Deploy Content Security Policies (CSP) to limit the execution of unauthorized scripts in browsers. Monitor logs for unusual activities related to GlobalBlocking functionalities and privileged user actions. Educate administrators about the risks of XSS and the importance of cautious input handling. Once patches become available from The Wikimedia Foundation, prioritize their deployment. Additionally, consider isolating or disabling the GlobalBlocking extension if it is not critical to operations to reduce the attack surface.