Summary
During a security assessment on a popular e-commerce platform, I stumbled upon a classic yet frequently overlooked vulnerability, an Integer Overflow leading to business logic bypass. By tampering with a simple quantity input field, I was able to break the backend’s pricing calculation and complete transactions for a grand total of ₹0. Here is how the flaw worked, why it happened, and how developers can prevent it. The Mechanics: Breaking the Math In 32-bit signed integer architecture, the maximum representable value is 2,147,483,647. When an application receives a number exceeding this limit without proper backend boundary checks, an integer overflow or unhandled exception occurs during arithmetic processing. In this instance, entering a quantity of 2147483649 caused the backend arithmetic engine to wrap or cast the value improperly. Instead of throwing a validation error, the system evaluated the item quantity as 0 . Because the backend calculated the total price using standard multiplication: Total Price = Unit Price x Quantity Multiplying any item price by 0 yielded a final order total of $0.00, allowing payment processing to be completely bypassed. Proof of Concept (Steps to Reproduce)
- Select an Item: Navigate to any product page on the platform and add the item to the cart.
- Intercept the Request: Go to the cart review page and capture the update-quantity request (via browser DevTools or an HTTP proxy like Burp Suite).
- Inject the Payload: Replace the existing quantity value with 2147483649 .
- Submit & Verify: Forward the request to the server. Get Rohit dalal’s stories in your inbox Join Medium for free to get updates from this writer.
- Exploit: The cart total updates to ₹0.00. Completing the checkout process generates a confirmed order without charging a payment card. Business Impact Business logic flaws of this nature represent a critical risk to e-commerce platforms. Exploitation requires no privileged access, and an attacker could leverage it to:
- Acquire high-value physical or digital assets for free.
- Exhaust inventory stocks rapidly, leading to denial-of-service for legitimate customers.
- Cause significant direct financial losses and accounting discrepancies. Remediation & Developer Takeaways Fixing integer-based business logic flaws requires defense-in-depth across input validation and data handling:
- Enforce explicit boundaries on quantity.
- Use safe Math functions and data types. 🔗 Connect with me on Linkedin ⚠️ Disclaimer This vulnerability was responsibly disclosed to the affected vendor prior to publication. The website has been notified, and all necessary actions have been taken. The author holds no further liability regarding the use, misuse, or consequences of this information.