An issue was discovered in MediaWiki before 1.37.3 and 1.38.x before 1.38.1. The contributions-title, used on Special:Contributions, is used as page title without escaping. Hence, in a non-default configuration where a username contains HTML entities, it won't be escaped.
https://www.debian.org/security/2022/dsa-5246
https://security.gentoo.org/glsa/202305-24
https://phabricator.wikimedia.org/T308473
https://lists.debian.org/debian-lts-announce/2022/09/msg00027.html