Business Logic Vulnerability: Price Manipulation

Introduction Business logic vulnerabilities are security weaknesses that exist in the way data and transactions are processed within an application. The most common, and dangerous type, is price manipulation, where there is exploitation of logical flaws in a certain e-commerce and financial systems wherein one buys products or services at a reduced or zero-cost basis. How Price Manipulation Works This happens when the application does not validate price information properly. This allows the attacker to change the price of the items just before finalizing the transaction. It could be a case of either client-side validation or API interaction or even database logic gone wrong. Popular Techniques for Price Manipulation 1. Tampering with Hidden Form Fields Many e-commerce platforms use hidden HTML form fields for storing price information. Attackers can use browser developer tools to change the price before submitting. Example:

• <inputtype=”hidden” name=”price” value=”100″>
• Changing the value from 100to 10 before submitting the form.

2. Intercepting and Modifying API Requests Latest web applications use API requests for pricing calculations. Attackers can use tools like Burp Suite to intercept API calls and modify price-related parameters before sending the request to the server. Example: { “product_id”: “12345”, “price”: “100.00” }

• Converting 00to 1.00 and sending to server.

3. Parameter Pollution Attacks Some applications do not handle multiple parameters correctly. Attackers can modify prices by adding extra parameters to confuse the server. Example:

• https://example.com/cart?product_id=12345&price=100&price=1
• The server may consider only the second price=1and charge $1 instead of $100 for the product.

4. Coupon and Discount Exploitation Some applications do not validate discount codes correctly or allow stacking of coupons up to their maximum limits. Attackers can apply unlimited discounts or reuse expired codes to reduce the price to zero. Example:

• Reusing Expired Codes: An attacker uses an expired code in the URL: https://example.com/checkout?product_id=12345&original_price=100&discount_code=SAVE50 Result: Final price is $50 instead of $100.
• Stacking Discounts: The attacker applies multiple valid discount codes: https://example.com/checkout?product_id=12345&original_price=100&discount_code=SAVE50&discount_code=SAVE30 Result: Final price is $35 instead of $100.
• Manipulating Discount Logic: The attacker modifies the discount code to 100%: https://example.com/checkout?product_id=12345&original_price=100&discount_code=SAVE100 Result: Final price is $0.

5. Currency Conversion Manipulation Some platforms allow users to switch currencies without validating exchange rates properly. Attackers can switch to a weaker currency, complete the transaction, and revert to their preferred currency at a higher rate. Example:

• Actual Price: A product costs $100 USD.
• Changing Currency: The user converts the currency to Indian Rupees (INR), where the price reads ₹8,000 (with an assumed conversion rate of ₹80 to 1 USD).
• Manipulating the Exchange Rate: The user finds that they can enter a custom exchange rate. They change the price to ₹1,000 (instead of the actual price).
• Completion of Transaction: The buyer makes the order, and the site takes the amount of ₹1,000 as payment for the item sold.

6. Cart Tampering & Race Conditions Few applications don’t validate the final price before completing the order process. Hackers can change cart information, create multiple requests, or change the session-based discounts to acquire any product without the cost. Example:

• An online retail shop that enables the customers to put a product into the cart and then discount it before submitting the order doesn’t check for final prices on orders submitted.
• Adding Products to Cart: A customer adds a very expensive product for $200.
• Applying Discounts: The customer can find a code that can get them a discount of 50%. Applying it, he expected the price should be $100.
• Manipulating the Cart: Before the checkout process is complete, the user rapidly manipulates the cart using browser developer tools to revert the item price back to $0 or some other significantly lower value.
• Making Multiple Requests: The user sends multiple requests to the server in rapid succession in an attempt to complete the purchase before the system processes the discount validation.
• Checkout Processing: If the server does not handle these requests properly, it might process one of the requests with the manipulated price of $0.

7. Changing Quantity to Manipulate Pricing If price manipulation fails, attackers can exploit the quantity parameter. By submitting a negative quantity along with a negative price, they can attempt to trick the system into providing products at no cost. Example: { “product_id”: “12345”, “price”: “-1000”, “quantity”: “-1” }

• the server could easily misinterpret it and thereby incur an accidental free transaction of items.

Example from Real Life A vulnerability in a popular online marketplace was found by a security researcher who manipulated the API request to adjust the price of digital goods sold through the website. They captured the payment request and changed the price of a $100 digital product to $0.10; the system did not check, and so they processed the transaction, leading to huge losses for the company until it could correct the flaw. The next example deals with a very popular online store for fashion clothes. The application has a weakness in their check-out system and attackers exploited this to raise the price of a designer coat from $500 to $5. They applied the change with the help of hidden input fields in the HTML. They ordered thousands of items in such a small period of time before the firm discovered the problem using an automated script. The retailer had to compensate several fraudulent orders and improve backend validation processes. How to Prevent Price Manipulation Attacks 1. Server-Side Validation Validate prices on the server-side and never trust values from the client-side. Store product prices securely in a backend database rather than relying on user input. 2. Use Secure API Design Implement digital signatures (HMAC) for the integrity of price-related API requests. Ensure that the backend side does the calculation rather than accepting prices from client requests. 3. Implement Strong Access Controls Restrict unauthorized users from accessing administrative or pricing-related functions. Use role-based access control (RBAC) to limit changes to critical financial data. 4. Monitoring and Transaction Logging Implement logging and anomaly detection to highlight unusual price modifications or bulk purchases. Use fraud detection systems for evaluating transaction patterns. 5. Control Coupon and Discount Abuse Limit the use of coupons on one transaction with strict validation on discount stacking. Include expired dates and ensure not to use any discount code twice. 6. Shield Against Race Conditions Implement atomic database transactions to prevent the manipulation of order prices through simultaneous requests. Locking mechanisms will be used to ensure price validation before checkout. Conclusion These vulnerabilities in the manipulation of prices, if not treated in the proper way, lead to huge losses in business operations. The attackers make use of various methods such as modifications in the form fields of the hidden form fields, API requests interception, and currency rate conversion for price alteration. Organizations must practice strong server-side validation and API security along with real-time monitoring to overcome such attacks on revenue.