Lecture on 403 Forbidden Response and Bypassing Techniques

Introduction

• 403 Forbidden responses often deter hackers, but they can indicate potential vulnerabilities.
• The lecture covers techniques to convert these dead ends into payouts in bug bounty programs.
• The importance of understanding access control failures to find significant bounties.
• Engagement Tip: Drop a lock emoji if you've encountered a 403 and suspected more beneath the surface.

Topics Covered

1. Why 403 Bypass Exists
2. Five Effective Bypass Techniques
3. Real Examples and Hands-On Labs

Why 403 Bypasses Exist

• Application Architecture: Multiple layers, like front-end (React) and back-end (APIs, gateways), create security gaps.
• Misunderstandings in access control, leading to exposed APIs and services.
• Importance of understanding architecture over relying solely on payloads.

Bypass Techniques

1. IP Address Bypasses

• Example: Secret endpoint denies access due to unknown IP.
  • Use headers like X-Forwarded-For with local IP (e.g., 127.0.0.1) or an app-specific IP.
• Automate header testing to identify anomalies and potential bypasses.

2. Path Normalization

• Accessing paths using different syntaxes:
  • Use ./admin instead of /admin.
  • Employ path traversal techniques (e.g., ../admin).
• Browser vs. curl: Browsers normalize paths, use tools like curl or web proxies for testing.

3. API Versioning

• Identify and test legacy API versions (e.g., v1, v1.1).
• Use web archives (Wayback Machine, GitHub) to find older API endpoints.

4. URL Encoding

• Encode portions of the URL to bypass restrictions (e.g., %2F for slashes).
• Double encoding strategies when initial encoding doesn't work.

5. Case Sensitivity

• Windows servers are case-insensitive, allowing bypasses by altering letter cases (e.g., Admin vs. admin).
• Critical for Windows-targeted hacking.

Practical Lab Insights

• Combine multiple techniques (path traversal, URL encoding) for effective bypasses.
• Understanding server behavior (Linux vs. Windows) aids in strategy formulation.

Conclusion

• Combining methods can uncover complex vulnerabilities.
• Encouragement to explore and experiment with different techniques.
• Call to engagement: Comment, like, subscribe for more content.