The Testimonial Post type plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the ‘auto_play’ parameter in all versions up to, and including, 1.2.1 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
https://wordpress.org/plugins/testimonial-post-type/#developers