Fluent Forms < 6.1.8 - Unauthenticated Payment Status Tampering via IDOR

Description

The plugin is vulnerable to Insecure Direct Object Reference 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.