Download Monitor < 5.1.8 - Insecure Direct Object Reference to Unauthenticated Arbitrary Order Completion via 'token' and 'order_id'

Description

The Download Monitor plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 5.1.7 via the executePayment() function due to missing validation on a user controlled key. This makes it possible for unauthenticated attackers to complete arbitrary pending orders by exploiting a mismatch between the PayPal transaction token and the local order, allowing theft of paid digital goods by paying a minimal amount for a low-cost item and using that payment token to finalize a high-value order.