This post is about my favorite category of bugs — business logic flaws. No scanner can find these. No tool. Only a curious human brain. Which means once you get good at these, you have an edge that automation can NEVER take from you.
What’s A Business Logic Flaw?
It’s not a coding bug like XSS or SQLi. It’s when the app does exactly what it was coded to do — but the LOGIC itself is broken. The rules of the business don’t make sense, and you abuse that.
No special characters. No payloads. Just using the app in a way the developers never imagined. 🧠
Real Examples That’ll Make It Click
The negative quantity: An online store lets you buy items. You change the quantity to -1. Instead of charging you, it CREDITS your account. Free money. 💰
The coupon stack: A 10%-off coupon is meant to be used once. You apply it 50 times. Now it’s 500% off.
The skipped step: Checkout is supposed to be: cart → payment → confirmation. You jump straight to confirmation, skipping payment. Free order.
The price tamper: You change the price field in the request from $100 to $1. The app trusts it. 😳
