FluentForm <= 5.1.16 is vulnerable to Authenticated (Contributor+) Stored Cross-Site Scripting vulnerability

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 the ‘subject’ parameter in versions up to, and including, 5.1.16 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level permissions and above, and access granted by an administrator, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.