Exploiting Business Logic Flaws in e-commerce platforms

Hey Hackers,

I am, back with another blog on breaking business logic! This time, I stumbled upon a fascinating series of flaws in an e-commerce platform for health tests. Initially, it all started with a simple parameter tampering exploit to reduce the price of a test. But as the developers patched one issue, new opportunities kept surfacing, pushing me to think creatively.

From tampering prices to exploiting negative quantities, this experience shows how business logic vulnerabilities can evolve with each patch attempt. Ready to see how persistence pays off?

So let’s start…

Introduction

Business logic vulnerabilities are among the most interesting bugs to discover. They require you to think beyond technical exploits and into the logic of how an application processes user input. These flaws allow attackers to exploit loopholes in the system’s workflow, often with devastating consequences.

In this blog, I’ll share my experience that started with a simple parameter tampering vulnerability and evolved into a series of bypasses across multiple patches. Each retest revealed a new angle of exploitation, demonstrating the persistence needed to uncover hidden weaknesses. By the end, I was able to manipulate the system to buy health tests worth thousands of rupees for just a fraction of the cost.

Initial Discovery – Exploiting the Price Parameter

It all began when I stumbled upon a parameter tampering vulnerability while testing a health test booking platform. The checkout request included several parameters, but the one that caught my attention was price.

During a routine test, I noticed that the price of a health test was set as 950 in the request payload. Intrigued, I decided to tamper with the value, changing it from 950 to 10.

When I sent the modified request, I was surprised to see the server accept it without any validation. The test was successfully added to my cart for just ₹10.

This discovery immediately raised alarm bells. A flaw in the way the application processed price values allowed me to purchase expensive tests at a ridiculously low cost. I reported this business logic flaw. They quickly responded by removing the price parameter from the request.

The First Retest – Manipulating the Quantity Parameter

After the initial patch, I decided to retest the application. Without the price parameter in the request, the system appeared more secure. However, I noticed that two parameters remained; Product_code and Quantity.

I decided to experiment with the quantity parameter. I added a test priced at ₹1600 to my cart. Then I manipulated the quantity value in the request, changing it from 1 to -1. To my astonishment, the server recalculated the test price as -₹1600.

Curious to explore further, I added another test worth ₹1800 to my cart. The final total during checkout was calculated as ₹200 instead of ₹3400.

This meant that by reducing the quantity to a negative value, I could offset the cost of more expensive tests and exploit the system for massive discounts. Once again, I reported this business logic flaw to the team. They quickly responded by removing the quantity parameter from the request altogether.

Second Retest

After the second patch, the quantity parameter was no longer visible in the request. However, I wasn’t convinced that the issue was fully resolved. I decided to manually add the quantity parameter back into the request using Burp Suite.

To my surprise, the server still processed the request, even with the manually added quantity field. I repeated the same process. Set the quantity to -1, Added products worth ₹1600 and ₹1800. The system once again recalculated the total to offset the negative value, allowing me to buy tests worth ₹3400 for just ₹200.

At this point, it became clear that the underlying validation mechanisms were still missing. I reported the issue again, emphasizing the need for server-side validation and input sanitization.

The development team responded to my second report by implementing a verification mechanism. This patch ensured that users could not purchase the same test more than once, effectively addressing the immediate issue.

This experience highlighted the importance of thorough patching and comprehensive validation to close all potential loopholes.

Lessons Learned

Server-Side Validation Is Key. The platform repeatedly failed to validate user input at the server level, allowing me to manipulate requests and parameters even after multiple patches.

Developers should implement multiple layers of security, including input validation, user authentication, and request verification, to prevent such vulnerabilities.

This journey through a series of business logic flaws highlights the importance of persistence in security testing. Each patch brought a new layer of challenge, but careful retesting revealed subtle weaknesses that could have been devastating if left unaddressed.

For developers, this serves as a reminder to think critically about how systems process user input. For security enthusiasts, it’s a testament to the value of digging deeper and always questioning whether a patch truly fixes the problem.

Happy hacking!