The Restrict Usernames Emails Characters WordPress plugin before 3.1.4 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Cross-Site Scripting attacks even when unfiltered_html is disallowed
https://wpscan.com/vulnerability/aba62286-9a82-4d5b-9b47-1fddde5da487/
https://github.com/youki992/youki992.github.io/blob/master/others/apply2.md