Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:9 relevant versions.
MediaWiki through 1.33.1 allows attackers to bypass the Title_blacklist protection mechanism by starting with an arbitrary title, establishing a non-resolvable redirect for the associated page, and using redirect=1 in the action API when editing that page.
mediawiki to version 1:1.27.7-1~deb9u3 or higher.