The Ninja Forms Contact Form WordPress plugin before 3.6.34 does not sanitize and escape its label fields, which could allow high privilege users such as admin to perform Stored XSS attacks. Only users with the unfiltered_html capability can perform this, and such users are already allowed to use JS in posts/comments etc however the vendor acknowledged and fixed the issue
https://wpscan.com/vulnerability/a642f313-cc3e-4d75-b207-1dceb6a7fbae