An issue was discovered in the FileImporter extension for MediaWiki before 1.34.4. An attacker can import a file even when the target page is protected against "page creation" and the attacker should not be able to create it. This occurs because of a mishandled distinction between an upload restriction and a create restriction. An attacker cannot leverage this to overwrite anything, but can leverage this to force a wiki to have a page with a disallowed title.
https://phabricator.wikimedia.org/T262628
https://gerrit.wikimedia.org/r/q/Ib852a96afc4dca10516d0510e69c10f9892b351b
https://commons.wikimedia.org/w/index.php?oldid=454609892#File:Wiki.png