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intermediate Phase · Backend Security

Authorization Bugs

Detect and prevent broken authorization vulnerabilities.

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Authorization Bugs Overview

Authorization bugs are among the most dangerous security vulnerabilities. They allow users to access data or perform actions they should not.

Common Authorization Bugs

  1. Broken Object Level Authorization (BOLA) - User A can access User B data by changing an ID
  2. Broken Function Level Authorization - Regular user accesses admin endpoints
  3. Missing Authorization - No permission check at all
  4. Excessive Data Exposure - API returns more data than user should see

Real-World Impact

Bug Type Impact
BOLA Data breach, privacy violation
Broken Function Auth Privilege escalation
Missing Auth Complete data exposure

Prevention Strategies

  1. Always check permissions before returning data
  2. Use consistent authorization middleware across all endpoints
  3. Test with multiple user roles during development
  4. Apply principle of least privilege

Defense Patterns

Authorization Check Examples

Always verify object ownership server-side:

  • Check that the authenticated user owns the resource
  • Use authorization annotations like @PreAuthorize
  • Never rely on client-side checks alone

Testing Authorization

Test Matrix:

Endpoint    | Owner | Other | Admin
GET /order  | Allow | Deny  | Allow
PUT /order  | Allow | Deny  | Deny
DELETE      | Allow | Deny  | Allow

Key Principles

  • Deny by default - require explicit permission
  • Check on every request - never cache auth decisions
  • Validate server-side - client-side checks are bypassable
  • Log all denials - for security auditing

Practice Problems

0 / 3 solved
Implement Authorization Bugs

Design and implement a solution for Authorization Bugs in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// Authorization Bugs implementation
// Key aspects: validation, error handling, logging, testing

public class AuthorizationBugs {
    // Production-ready implementation
}
Authorization Bugs Edge Cases

Identify and handle edge cases for Authorization Bugs. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
Authorization Bugs Testing Strategy

Write a testing strategy for Authorization Bugs. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. What is BOLA?

Question 1 options

2. How to prevent authorization bugs?

Question 2 options

3. What is a common mistake when implementing Authorization Bugs?

Question 3 options

Flashcards

Question

What is BOLA?

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Answer

Broken Object Level Authorization - accessing others data via ID manipulation

Question

How to prevent auth bugs?

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Answer

Deny by default, check every request, validate server-side

Question

Authorization Bugs best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. BOLA is the most common API security vulnerability
  • 2. Always check object ownership before returning data
  • 3. Use deny-by-default policy
  • 4. Test authorization with multiple user roles

Interview Tips

  • • Explain how you would test for BOLA
  • • Discuss the difference between authentication and authorization

Cheat Sheet

Authorization Bugs

  • BOLA: Access others data via ID manipulation
  • Prevention: Deny by default, check every request
  • Testing: Matrix of users x endpoints
  • Logging: Record all denials for audit