The Fluent Forms – Customizable Contact Forms, Survey, Quiz, & Conversational Form Builder plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 6.1.7 via the 'submission_id' parameter due to missing validation on a user controlled key within the confirmScaPayment() function. This makes it possible for unauthenticated attackers to mark arbitrary submissions as failed via crafted requests to the endpoint granted they can guess or enumerate a valid submission identifier.