An issue was discovered in the FileImporter extension in MediaWiki through 1.36. For certain relaxed configurations of the $wgFileImporterRequiredRight variable, it might not validate all appropriate user rights, thus allowing a user with insufficient rights to perform operations (specifically file uploads) that they should not be allowed to perform.
Mediawiki before 1.28.1 / 1.27.2 contains an unsafe use of temporary directory, where having LocalisationCache directory default to system tmp directory is insecure.
An issue was discovered in the Widgets extension for MediaWiki through 1.35.1. Any user with the ability to edit pages within the Widgets namespace could call any static function within any class (defined within PHP or MediaWiki) via a crafted HTML comment, related to a Smarty template. For example, a person in the Widget Editors group could use \MediaWiki\Shell\Shell::command within a comment.