MediaWiki before 1.23.11, 1.24.x before 1.24.4, and 1.25.x before 1.25.3 does not properly restrict access to revisions, which allows remote authenticated users with the viewsuppressed user right to remove revision suppressions via a crafted revisiondelete action, which returns a valid a change form.
https://phabricator.wikimedia.org/T95589
https://lists.wikimedia.org/pipermail/mediawiki-announce/2015-October/000181.html