Citizen is a MediaWiki skin that makes extensions part of the cohesive experience. The citizen-search-noresults-title and citizen-search-noresults-desc system messages are inserted into raw HTML, allowing anybody who can edit those messages to insert arbitrary HTML into the DOM. This vulnerability is fixed in 3.3.1.
https://github.com/StarCitizenTools/mediawiki-skins-Citizen/security/advisories/GHSA-86xf-2mgp-gv3g