CVE-2025-53370 is a high-severity Cross-site Scripting (XSS) vulnerability identified in the Citizen skin for MediaWiki, a popular platform for collaborative content management. The Citizen skin integrates various MediaWiki extensions to provide a cohesive user experience. The vulnerability affects versions from 1.9.4 up to but not including 3.4.0. Specifically, the issue arises because short descriptions set via the ShortDescription extension are inserted into the web page as raw HTML without proper sanitization or encoding. This improper neutralization of input (CWE-79) allows any user with the ability to edit pages to inject arbitrary HTML and potentially malicious JavaScript code into the Document Object Model (DOM). The vulnerability does not require authentication or user interaction to be exploited, and the attack vector is network-based, meaning an attacker can exploit it remotely. The CVSS v3.1 score of 8.6 reflects the high impact on confidentiality and availability, with limited impact on integrity. Successful exploitation could lead to theft of user credentials, session hijacking, defacement, or distribution of malware to users visiting the affected wiki pages. Although no known exploits are currently reported in the wild, the vulnerability has been publicly disclosed and patched in version 3.4.0 of the Citizen skin. Organizations using affected versions should consider this a critical security risk due to the ease of exploitation and the potential for widespread impact on users and data integrity.

For European organizations utilizing MediaWiki with the Citizen skin, this vulnerability poses significant risks. Many public sector entities, educational institutions, and enterprises in Europe rely on MediaWiki for documentation and knowledge sharing. Exploitation could lead to unauthorized disclosure of sensitive information, especially if internal wikis are accessible externally or to a broad user base. The injection of malicious scripts could facilitate phishing attacks, credential theft, or malware distribution, undermining user trust and potentially causing reputational damage. Additionally, the availability of wiki resources could be disrupted by injected scripts causing denial of service or content manipulation. Given the collaborative nature of wikis, the vulnerability could be exploited by insiders or external attackers who gain editing privileges, amplifying the threat. The impact is heightened in regulated sectors such as finance, healthcare, and government, where data confidentiality and integrity are paramount and compliance with GDPR and other regulations is mandatory.

To mitigate this vulnerability, European organizations should promptly upgrade the Citizen skin to version 3.4.0 or later, where the issue is patched. Until the upgrade is applied, organizations should restrict editing permissions to trusted users only, minimizing the risk of malicious input. Implementing Content Security Policy (CSP) headers can help reduce the impact of injected scripts by restricting the sources of executable code. Additionally, organizations should audit existing wiki pages for suspicious or unexpected HTML content in short descriptions and remove any potentially malicious code. Regularly monitoring wiki logs for unusual editing activity can help detect exploitation attempts early. Where possible, deploying web application firewalls (WAFs) with rules targeting XSS payloads can provide an additional layer of defense. Finally, educating users about the risks of XSS and safe editing practices will help reduce inadvertent introduction of vulnerabilities.