Citizen is a MediaWiki skin that makes extensions part of the cohesive experience. A user with the editmyprivateinfo right or who can otherwise change their name can XSS themselves by setting their "real name" to an XSS payload. This vulnerability is fixed in 2.31.0.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.008
EPSS Ranking 73.6%