Quantity Manipulation Allows Purchases at Reduced Prices

Description

During a penetration testing engagement at CyberAR, I discovered a critical vulnerability that allows attackers to purchase products at significantly reduced prices through quantity manipulation.

Exploit Begins

While exploring the website, I identified it as an online store selling various products. After completing some initial test cases, I navigated to the product section to conduct further testing.I selected a product and intercepted the request when I clicked “Add to Cart” to examine the associated request

I noticed a parameter labeled “quantity” which determines the number of items to purchase. I attempted to manipulate this parameter by changing its value from 1 to 0.5 Although the response didn’t indicate any changes, I added the product to my cart and then opened my cart to proceed. I decided to test the item update function.

Next, I intercepted the request and increased the quantity to 2. Upon reviewing the request, I noticed the quantity parameter along with some different parameters compared to the previous request. I then changed the quantity from 2 to 0.5 and observed a price reduction from $3000 to $1500.

To realize a greater effect of this vulnerability, I repeated the process, adjusting the quantity to an even smaller value of 0.01

When I clicked on checkout, I noticed the price changed to $30, with an additional $80 for shipping, bringing the total to $110 instead of the original $3080.

To clarify further, the product price is $3000. When I increase the quantity, the price adjusts accordingly:

For a quantity of 2: $3000 * 2 = $6000For a quantity of 0.5: $3000 * 0.5 = $1500For a quantity of 0.01: $3000 * 0.01 = $30

However, I needed to confirm whether this was just a user interface (UI) issue, so I continued with the purchasing process. I entered payment information that did not contain sufficient funds to cover the full amount. Upon clicking “Place Order,” I received a notification indicating that the transaction was successful at $110, rather than the expected $3080. The order was ultimately declined due to insufficient funds on the card.

Test Case for Financial Loss Calculation

Objective: To determine the financial loss incurred by the company due to the exploitation of the vulnerability.

Assumption:

Number of users: 100

Details:

Total original price of products: $74,718Price after exploiting the vulnerability: $747.18

Calculations:

Calculate the total original price for 100 users:74,718 × 100 = $7,471,800

2. Calculate the total price for 100 users after using the vulnerability:

747.18 × 100 = $74,718

3. Calculate the total financial loss:

7,471,800 − 74,718 = $7,397,082

Total Financial Loss:

The total financial loss incurred by the company is $7,397,082

Summary

This discovery highlights a significant security vulnerability related to quantity manipulation in the purchasing process. Attackers could exploit this flaw to acquire products at greatly reduced prices, which poses a serious risk to the integrity of the online store and its revenue. Immediate action is necessary to address and remediate this vulnerability.