In MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4, XSS related to jQuery can occur. The attacker creates a message with [javascript:payload xss] and turns it into a jQuery object with mw.message().parse(). The expected result is that the jQuery object does not contain an <a> tag (or it does not have a href attribute, or it's empty, etc.). The actual result is that the object contains an <a href ="javascript... that executes when clicked.

References:
https://lists.wikimedia.org/pipermail/mediawiki-l/2020-September/048480.html
https://lists.wikimedia.org/pipermail/mediawiki-l/2020-September/048488.html
https://www.mediawiki.org/wiki/ResourceLoader/Core_modules#mediawiki.jqueryMsg