CVE-2025-53487 is a stored Cross-Site Scripting (XSS) vulnerability affecting the ApprovedRevs extension of the MediaWiki platform maintained by the Wikimedia Foundation. The vulnerability arises from improper neutralization of input during web page generation (CWE-79), specifically where system messages are inserted into raw HTML without adequate escaping. Attackers can exploit this flaw by leveraging the 'uselang=x-xss' language override parameter to inject crafted message keys containing malicious JavaScript payloads. These payloads are then rendered unescaped in multiple locations within the MediaWiki interface, leading to persistent XSS conditions. The affected versions include MediaWiki ApprovedRevs extension releases from 1.39.x prior to 1.39.13, 1.42.x prior to 1.42.7, and 1.43.x prior to 1.43.2. This vulnerability allows attackers to execute arbitrary JavaScript in the context of the victim's browser session, potentially leading to session hijacking, credential theft, unauthorized actions, or distribution of malware. Although no known exploits are currently reported in the wild, the vulnerability's nature and ease of exploitation via a URL parameter make it a significant risk for any MediaWiki deployments using the ApprovedRevs extension. The absence of a CVSS score indicates that the vulnerability is newly disclosed and pending formal severity assessment.

For European organizations utilizing MediaWiki with the ApprovedRevs extension, this vulnerability poses a substantial risk to confidentiality, integrity, and availability of information. Exploitation could allow attackers to hijack user sessions, steal sensitive credentials, or perform unauthorized actions within the wiki environment, potentially compromising internal documentation, intellectual property, or collaborative content. Public-facing wikis used by government agencies, educational institutions, or enterprises could be manipulated to serve malicious scripts to visitors, damaging reputation and trust. Additionally, attackers could leverage the vulnerability to pivot into broader network attacks if the wiki integrates with internal systems. The persistent nature of stored XSS increases the risk as malicious scripts remain active until the injected content is removed or patched. Given the widespread use of MediaWiki in Europe, especially in public sector and academic environments, the impact could be significant if not addressed promptly.

To mitigate this vulnerability, organizations should immediately upgrade the ApprovedRevs extension to the fixed versions: 1.39.13 or later for the 1.39.x branch, 1.42.7 or later for the 1.42.x branch, and 1.43.2 or later for the 1.43.x branch. If upgrading is not immediately feasible, administrators should disable the 'uselang' parameter override or implement strict input validation and output encoding to prevent unescaped HTML rendering of system messages. Employing Content Security Policy (CSP) headers can help mitigate the impact of injected scripts by restricting script execution sources. Regularly auditing MediaWiki extensions for security updates and monitoring logs for suspicious URL parameters or message keys is recommended. Additionally, user education on phishing and suspicious links can reduce the risk of exploitation via crafted URLs. Finally, restricting access to the wiki to trusted users and networks can limit exposure.