Exploiting Business Logic: Inventory Depletion via Parameter Tampering

Censorship Note: To strictly protect the identity of the affected program, all identifiers, variables, grace periods, API paths, and internal mechanics have been abstracted or replaced with generic concepts (e.g., METHOD_A, /checkout/gateway). Any resemblance to a real-world platform is purely structural for the theoretical understanding of the flaw.

This writeup documents a critical Business Logic Error (CWE-840) discovered in the payment flow of an event-driven e-commerce platform.

The exploitation chained a session cart limit bypass with parameter tampering at the payment gateway level, allowing an attacker to reserve and entirely deplete an event's available stock without processing any real payment.

Architecture and Deficiencies

The legitimate reservation and payment flow dictated the following steps:

1. The user adds the desired quantity to their cart (both frontend and backend should limit this to a small fraction of the total).