Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:unstable relevant versions.
An issue was discovered in MediaWiki before 1.31.12 and 1.32.x through 1.35.x before 1.35.2. On Special:NewFiles, all the mediastatistics-header-* messages are output in HTML unescaped, leading to XSS.
mediawiki to version 1:1.35.2-1 or higher.