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CVE-2025-53479: CheckUser: Reflected Cross-Site Scripting (XSS) in Special:CheckUser via unsanitized internationalized message
Description
The CheckUser extension’s Special:CheckUser interface is vulnerable to reflected XSS via the rev-deleted-user message. This message is rendered without proper escaping, making it possible to inject JavaScript through the uselang=x-xss language override mechanism.
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.
Classification
CVE ID: CVE-2025-53479
Problem Types
CWE-79 Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting')Affected Products
Vendor: Wikimedia Foundation
Product: Mediawiki - CheckUser extension
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.03% (probability of being exploited)
EPSS Percentile: 6.3% (scored less or equal to compared to others)
EPSS Date: 2025-07-10 (when was this score calculated)
References
https://nvd.nist.gov/vuln/detail/CVE-2025-53479https://phabricator.wikimedia.org/T394693
https://gerrit.wikimedia.org/r/q/I159e14543912cb3bc7f4a00c3090c0285b154786