The Contact Form Plugin by Fluent Forms for Quiz, Survey, and Drag & Drop WP Form Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via form label fields in all versions up to, and including, 5.1.19 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with access to edit forms (administrator by default), to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
https://plugins.trac.wordpress.org/changeset/3125227/
https://plugins.trac.wordpress.org/browser/fluentform/tags/5.1.17/boot/globals.php#L342