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.
CWE-862 - Missing Authorization
The missing authorization vulnerability occurs when a software program allows users to access privileged parts of the program without verifying the user credentials. Impact of such a vulnerability depends on the resources employed by the software, ranging from account takeover to sensitive information exposure, denial of service, and complete system takeover.