IDOR: What Is It and How Does One URL Change Expose Every User's Data?

What Is IDOR and How Does One URL Change Expose Every User's Data?

IDOR, or Insecure Direct Object Reference, is one of the most common and easy-to-miss access control flaws in web applications. It happens when a server uses a value from the user, like a number in the URL, to fetch records without checking if that user is allowed to see them. No special tools needed, just a number change in the address bar.

Brief Introduction

When your profile loads at a URL like this:

http://<target>/profile?user_id=51