Mediawiki before 1.28.1 / 1.27.2 / 1.23.16 contains a flaw allowing to evade SVG filter using default attribute values in DTD declaration.
https://security-tracker.debian.org/tracker/CVE-2017-0366
https://phabricator.wikimedia.org/T151735
https://lists.wikimedia.org/pipermail/mediawiki-announce/2017-April/000207.html