Fixing Business Logic Bypass

TL;DR

A business logic bypass lets someone do something they shouldn’t be able to in your application (like get a discount when they don’t have a code). This guide shows you how to find and fix these issues by carefully checking your code, adding more security checks, and testing thoroughly.

Understanding Business Logic Bypass

Business logic is the set of rules that makes your application work. A bypass happens when someone finds a way around those rules. For example:

• Discount Codes: Applying a code multiple times, or using an expired code.
• Permissions: Accessing features they shouldn’t be able to (e.g., viewing admin pages).
• Pricing: Manipulating prices during checkout.

How to Find Business Logic Bypass Issues

1. Code Review: Carefully look through your code, especially parts that handle important business rules (discounts, payments, permissions). Look for assumptions and missing checks.
2. Threat Modeling: Think like an attacker! What are all the ways someone could try to break your rules? Document these scenarios.
3. Input Validation: Always check user input. Don’t trust anything coming from the client-side.
   • Data Type: Is it a number when you expect text?
   • Range: Is it within acceptable limits (e.g., age between 0 and 120)?
   • Format: Does it match the expected pattern (e.g., email address format)?
4. Fuzzing: Use tools to automatically send lots of different inputs to your application, looking for crashes or unexpected behaviour.
5. Penetration Testing: Hire a security expert to try and find vulnerabilities in your system.

Fixing Business Logic Bypass Issues

1. Implement Strong Validation: Add checks at every layer of your application (client-side, server-side, database).
   • Server-Side is Crucial: Client-side validation can be bypassed easily.
2. Use Authorisation Checks: Make sure users only have access to the features they are allowed to use.

   // Example in Python (Flask)
   from flask import Flask, request
   
   app = Flask(__name__)
   
   @app.route('/admin/panel')
   def admin_panel():
     if not request.authorization or request.authorization['username'] != 'admin':
       return "Unauthorized", 401
     return "Admin Panel Access Granted!"
   

3. Enforce Business Rules: Clearly define and enforce your business rules in your code.

   // Example JavaScript (Node.js)
   function applyDiscount(price, discountCode) {
     if (!discountCode || discountCode !== 'SUMMER20') {
       return price; // No discount applied
     }
     const discountedPrice = price * 0.8;
     return discountedPrice;
   }
   

4. Avoid Direct Database Manipulation: Use prepared statements or an ORM to prevent SQL injection and other database-related attacks.
5. Rate Limiting: Limit the number of requests a user can make in a certain time period. This can help prevent brute-force attacks.
6. Logging & Monitoring: Log important events (e.g., failed login attempts, unauthorized access) and monitor your system for suspicious activity.

Testing Your Fixes

1. Unit Tests: Test individual components of your code to make sure they are working correctly.
2. Integration Tests: Test how different parts of your application work together.
3. End-to-End Tests: Test the entire application from start to finish, simulating real user behaviour.
4. Regression Testing: After fixing a bug, re-run all your tests to make sure you haven’t introduced any new issues.

Resources

• OWASP Business Logic Bypass: https://owasp.org/www-project-top-ten/