Course 1 - BurpSuite Bug Bounty Web Hacking from Scratch | Episode 7: Insecure Direct Object Reference (IDOR): Understanding, Testing

In this lesson, you’ll learn about:IDOR (Insecure Direct Object Reference) — definition: when user-supplied references (IDs) let attackers access or modify objects they’re not authorized to (files, records, accounts).Core mechanism: the app trusts the client-supplied identifier instead of enforcing authorization checks on the server side.Simple IDOR testing (numeric IDs): try adjacent or sequential IDs (e.g., /user=123 → /user=124) and watch for different responses.Automation of basic tests: use tools like Burp Intruder with a numeric payload (start/stop/step) and monitor response lengths/status for differences.Detection signals: changing content length, differing response bodies, or absence/presence of access-denied messages indicate possible IDOR.Advanced IDOR — obscured IDs (UUIDs): UUIDs are hard to guess; testing requires finding where the UUID leaks (page source, API responses, invitation flows, team endpoints).Techniques to find UUID leaks: inspect page source, JSON responses, invitation links, or any client-side data that may expose identifiers.Impact & reporting: even non-guessable IDs are valid findings if sensitive data can be accessed; explain impact clearly to evaluators.Practical demo — file access IDOR: intercept a request (e.g., source_viewer.php?file=user_file.php), modify the file parameter to an unauthorized target (e.g., index.php) and observe source disclosure.Mitigations: enforce server-side authorization checks for every object access, use indirect references or per-user mapping, avoid predictable IDs in URLs, and implement least privilege for object access.Analogy (teaching aid): like a hotel key coded with a room number — if you can change the number on your key and open other rooms, the system is IDOR-vulnerable.You can listen and download our episodes for free on more than 10 different platforms:https://linktr.ee/cybercode_academy