CVE-2025-53093 is a high-severity cross-site scripting (XSS) vulnerability affecting the TabberNeue extension for MediaWiki, developed by StarCitizenTools. This extension enables the creation of tabbed content within MediaWiki pages. The vulnerability exists in versions 3.0.0 up to but not including 3.1.1. It arises from improper neutralization of input during web page generation, specifically allowing any user to inject arbitrary HTML into the Document Object Model (DOM) by inserting malicious payloads into any permitted attribute of the <tabber> tag. This flaw corresponds to CWE-79 (Improper Neutralization of Input During Web Page Generation) and CWE-80 (Improper Neutralization of Script-Related HTML Tags). Exploitation does not require authentication or user interaction, and the attack vector is network-based, making it remotely exploitable. The vulnerability has a CVSS v3.1 base score of 8.6, indicating high severity, with impact metrics showing high confidentiality impact, low integrity impact, and low availability impact. Although no known exploits are currently reported in the wild, the vulnerability allows attackers to execute arbitrary scripts in the context of the affected MediaWiki site, potentially leading to session hijacking, data theft, or further attacks against users and administrators. The issue was patched in version 3.1.1 of the extension, which properly sanitizes input to prevent injection of malicious HTML. Organizations using affected versions should upgrade promptly to mitigate risk.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on MediaWiki platforms with the TabberNeue extension for internal or public knowledge bases, documentation, or collaboration portals. Successful exploitation could lead to unauthorized disclosure of sensitive information, including user credentials and internal data, through session hijacking or cookie theft. Additionally, attackers could manipulate the content displayed to users, potentially distributing malware or phishing content, undermining trust and damaging organizational reputation. The vulnerability could also facilitate lateral movement within networks if attackers leverage stolen credentials or session tokens. Given that MediaWiki is widely used in academic, governmental, and corporate environments across Europe, the risk extends to critical sectors such as education, public administration, and technology companies. The lack of required authentication for exploitation increases the threat surface, allowing external attackers to target vulnerable installations directly. Although availability impact is rated low, the integrity and confidentiality breaches pose serious compliance and operational risks under European data protection regulations such as GDPR.

To mitigate this vulnerability, European organizations should immediately upgrade the TabberNeue extension to version 3.1.1 or later, where the input sanitization flaw has been fixed. If upgrading is not immediately feasible, organizations should implement strict input validation and sanitization at the application layer to block malicious payloads targeting the <tabber> tag attributes. Employing a Web Application Firewall (WAF) with custom rules to detect and block suspicious HTML or script injections targeting MediaWiki pages can provide interim protection. Regularly audit MediaWiki extensions and configurations to ensure they are up to date and securely configured. Additionally, organizations should monitor web server logs for unusual requests containing suspicious payloads and educate users about the risks of XSS attacks. Implementing Content Security Policy (CSP) headers can also reduce the impact of successful script injections by restricting the execution of unauthorized scripts. Finally, conduct periodic security assessments and penetration testing focused on web application vulnerabilities to proactively identify and remediate similar issues.