CVE-2025-53480: Wikimedia Foundation Mediawiki - Checkuser Extension

Medium severity, CVSS 5.4. EPSS: 0.2% chance of exploitation in the next 30 days.

The CheckUser extension’s Special:Investigate page has a vulnerability in the Account information tab, where specific internationalized messages are rendered without proper escaping. Attackers can exploit this by appending ?uselang=x-xss to the URL, causing reflected XSS when the UI renders affected message keys. This issue affects Mediawiki - CheckUser extension: from 1.39.X before 1.39.13, from 1.42.X before 1.42.7, from 1.43.X before 1.43.2.

Affected products

• Wikimedia Foundation Mediawiki - Checkuser Extension: from 1.39, before 1.39.13 (fixed in 1.39.13); from 1.42, before 1.42.7 (fixed in 1.42.7); from 1.43, before 1.43.2 (fixed in 1.43.2)

Published 2025-07-08. Last modified 2026-06-17.