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๐Ÿšจ Broken Function Level Authorization โ€“ API5:2023 ๐Ÿ”“

March 25, 2025

I'm kicking off a

series of articles on API Security

๐Ÿ” to help usโ€”

developers

๐Ÿ‘จ๐Ÿ’ป๐Ÿ‘ฉ๐Ÿ’ปโ€”better understand and implement

secure coding

in our software design. ๐Ÿ›ก๏ธ


Here is the fifth one: Broken Function Level Authorization


APIs expose functions that allow users to interact with systems. But what happens when authorization controls are weak? Attackers can exploit APIs to access admin functions, modify data, or escalate privileges beyond what they should have. ๐Ÿšจ


โš ๏ธ What is Broken Function Level Authorization?

This vulnerability occurs when APIs fail to properly enforce role-based access controls (RBAC), allowing users to:

  • Access admin-only endpoints ๐Ÿ›‘ โ€“ A regular user calls an admin function.
  • Perform unauthorized actions ๐Ÿšซ โ€“ Example: A user escalates their own privileges.
  • Modify business logic โš™๏ธ โ€“ Example: Changing order prices, bypassing limits.


๐Ÿ” How Does It Happen?

๐Ÿšซ Inconsistent authorization checks โ€“ Some endpoints enforce RBAC, others donโ€™t.

๐Ÿšซ Predictable URL patterns โ€“ Example: /admin/deleteUser is accessible with a simple role change.

๐Ÿšซ Client-side role enforcement โ€“ Attackers modify requests to bypass UI restrictions.

๐Ÿšซ Missing privilege separation โ€“ Regular users can access high-privilege functions.


๐ŸŽฏ Real-World Risks:

โœ… Data exposure โ€“ Unauthorized access to sensitive information ๐Ÿ“‚

โœ… Privilege escalation โ€“ Attackers gain admin capabilities ๐Ÿ”‘

โœ… Business logic abuse โ€“ Users modify data without permission ๐Ÿฆ


๐Ÿ›ก๏ธ How to Prevent It?

๐Ÿ”ธ Enforce RBAC & ABAC ๐Ÿ” โ€“ Implement strict role-based access at every level.

๐Ÿ”ธ Deny by default โŒ โ€“ Restrict access unless explicitly permitted.

๐Ÿ”ธ Perform server-side authorization checks ๐Ÿ›ก๏ธ โ€“ Never trust client-side roles.

๐Ÿ”ธ Use least privilege principle โš–๏ธ โ€“ Users should only access what they need.

๐Ÿ”ธ Monitor API access logs ๐Ÿ“Š โ€“ Detect and block unauthorized access attempts.

๐Ÿš€ APIs should respect user roles, not just assume them!

#APISecurity #OWASP #CyberSecurity #RBAC #SecureCoding #Authorization