Hustle < 7.8.14.2 - Unauthenticated Arbitrary Shortcode Execution via Success Message Placeholders

Description

The plugin does not prevent shortcodes in submitted form values from being executed when it substitutes those values into the message it returns after submission, because the guard it applies can be defeated by nesting, allowing unauthenticated users to run any shortcode registered on the site.
Exploitation requires the site to have configured that message to include one of the submitted values.