Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:9 relevant versions.
In MediaWiki before 1.31.8, 1.32.x and 1.33.x before 1.33.4, and 1.34.x before 1.34.2, private wikis behind a caching server using the img_auth.php image authorization security feature may have had their files cached publicly, so any unauthorized user could view them. This occurs because Cache-Control and Vary headers were mishandled.
mediawiki to version 1:1.27.7-1~deb9u7 or higher.