Question 1

What is an IDOR vulnerability?

Accepted Answer

IDOR (Insecure Direct Object Reference) is an authorization vulnerability that allows access to other users' resources by modifying an identifier in the URL or request (e.g. /api/documents?id=1234 → /api/documents?id=1235). It exposes personal data, invoices, or medical records depending on the context.

Question 2

How does an IDOR attack work?

Accepted Answer

The attacker identifies a predictable parameter in a URL or API request (a number, an incremental UUID) and changes it to access other users' resources. Without a server-side authorization check, the system returns any user's data to anyone who knows their identifier.

Question 3

How do you fix an IDOR vulnerability?

Accepted Answer

To fix IDOR: systematically verify server-side that the authenticated user owns the requested resource, use unpredictable identifiers (random UUID v4 rather than sequential integers), implement role-based access control (RBAC), and test with tools like Burp Suite.

Question 4

Is IDOR in the OWASP top list?

Accepted Answer

Yes, IDOR falls under category A01:2021 — Broken Access Control in the OWASP Top 10 2021, ranked as the most widespread and dangerous web vulnerability. It has caused major data leaks at Facebook, Instagram, Parler, and numerous healthcare platforms.

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