HardExperience level: 8-15 years1 min read

What are the top API security risks (OWASP API), and how do you prevent BOLA?

Reviewed by Gurusankar M.

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#api security#owasp#bola#idor#authorization
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Short Answer

The #1 OWASP API risk is BOLA/IDOR — Broken Object Level Authorization: a user requests /orders/{id} for an id they don't own and the server returns it because it only checks authentication, not ownership. Prevent it by enforcing per-object authorization on every request, server-side.

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“What are the top API security risks (OWASP API), and how do you prevent BOLA?”

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Mind Map Answer

BOLA/IDOR
access others' objects by guessing ids
Cause
auth check ≠ ownership check
Fix
verify caller owns/can access THIS object
Also
broken auth, excessive data exposure, no rate limit

Think Beyond the Expected

What If?

Does using a random UUID instead of a sequential id fix BOLA?

No — that's security by obscurity. UUIDs are harder to guess but still leak (logs, referrals, shared links). The real fix is an authorization check: does THIS authenticated user have the right to THIS object? Enforce it on every read/write, never trust the id alone.

Real World

BOLA is the most common and damaging real-world API vulnerability (mass data exposure by iterating ids). The durable fix is centralized per-object authorization, often verified by automated tests that try cross-tenant access.

Interviewer's Expectation

Keywords they're listening for:

  • BOLA/IDOR #1
  • authN vs object-level authZ
  • check ownership per request
  • UUID ≠ fix
  • OWASP API top risks

Common Mistakes

  • Checking authentication but not ownership
  • Relying on unguessable ids for security
  • Returning full objects (excessive data exposure)

Best Practices

  • Enforce object-level authorization everywhere
  • Centralize authZ; test cross-tenant access
  • Return only needed fields (DTOs)

Follow-up Questions

  1. Why is UUID not an authorization control?
  2. How do you test for BOLA automatically?
  3. What are excessive data exposure and mass assignment?

References

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I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner.

Topic: Auth (REST APIs)
Interview question: "What are the top API security risks (OWASP API), and how do you prevent BOLA?"

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1. Explain the core idea in simple, plain language, using an everyday analogy.
2. Define any technical terms you use.
3. Walk through one small, concrete example.
4. Finish with a single sentence I can easily remember.

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