# Business Logic Security Vulnerabilities: Price Manipulation and Coupon Abuse

**URL:** https://securesys.com.tr/en/learning/web-application-security/business-logic-security-vulnerabilities

### What Are Business Logic Vulnerabilities?

![Business logic security vulnerabilities: price manipulation and coupon abuse](/images/bilgi-merkezi/covers/cover-business-logic.webp)

A web application may technically pass every security control — it may have no SQL Injection, its XSS vulnerabilities may be fixed, and its authentication may be securely configured. Yet the application can still be open to attack because its business processes are poorly designed or insufficiently checked.

**Business logic vulnerabilities** are weaknesses arising from gaps in the application's operating rules that allow attackers to use the system in ways the developer did not anticipate. The problem is not in the technology used, but in the difference between how the application "should work" and how it "actually works".

### Why Do Automated Security Tools Miss These Vulnerabilities?

Automated tools can quickly scan for predefined technical vulnerabilities such as SQL Injection or XSS. However, an automated tool cannot answer questions like: how many times can a user redeem the same discount coupon? Is an order confirmed even though payment failed? Can the same campaign be abused with different accounts? The answers to these questions can only be found through the manual analysis of experienced penetration testers who understand how the application works.

### The Most Common Business Logic Vulnerabilities

#### \1. Price Manipulation

Some applications calculate the product price based on data sent by the client. If there is no server-side validation, the attacker can modify the request to buy a product far below its real value — for example, manipulating the request `{"productId": 2501, "price": 1500}` to `{"productId": 2501, "price": 15}`.

#### \2. Campaign and Coupon Abuse

The same coupon being usable across different sessions, race conditions being altered, or expired coupons becoming active again all lead directly to revenue loss.

#### \3. Bypassing the Process Order

In a sequential flow such as Basket → Address → Payment → Order Confirmation, if the attacker can send the request for the final step directly, the process is bypassed. Such vulnerabilities can have critical consequences, especially in payment systems.

#### \4. Race Condition

When the same operation is submitted concurrently multiple times, the application may behave unexpectedly — the same gift card being used twice, a balance being spent twice, or the same product being deducted from stock more than once.

### A Real-World Scenario

On an online sales platform, order creation and payment were handled by separate services. During the penetration test it was found that even when the payment request was cancelled, the order service did not verify this. As a result, a user could create an order without paying, the order moved to "successful" status, and the logistics process started automatically. Even though the system had no classic vulnerabilities such as SQL Injection, XSS or RCE, this single flaw in the workflow created a serious risk of financial loss.

### SecureSys Business Logic Testing Approach

Our tests cover step-by-step verification of workflows, analysis of permission and role changes, testing of payment and order processes, examination of campaign/coupon mechanisms, and the creation of race-condition scenarios. This approach reveals critical business logic vulnerabilities in applications that appear technically secure.

### Business Logic Flaws and Their Potential Outcomes

| Business Logic Flaw | Potential Outcome |
| --- | --- |
| A discount coupon being reusable | Revenue loss |
| Product price alterable on the client side | Financial damage |
| The payment step being skippable | Unauthorised orders |
| Bypassing the approval process | Unauthorised operations |

Detecting business logic vulnerabilities requires an experienced manual testing team — reach out via our [Web Application Penetration Testing Service](/en/services/web-application-security-test-service) page.