Day 8 — Insecure Direct Object Reference (IDOR) Vulnerability in Web Applications: A Practical Demonstration with Flask

This technical document explores the Insecure Direct Object Reference (IDOR) vulnerability, a critical issue in web application security classified under Broken Access Control in the OWASP Top 10. Through a hands-on example using Python and the Flask framework, we demonstrate how IDOR can arise from improper authorization checks, allowing unauthorized access to sensitive data. The document follows a "build → break → fix" methodology: constructing a vulnerable application, exploiting the flaw, and implementing remediation strategies. Additional details on underlying concepts, real-world implications, and best practices are provided to enhance understanding for developers and security practitioners. Key concepts covered include authentication vs. authorization, URL parameter manipulation, and secure design patterns. Code examples are in Python 3.x with Flask 2.x, assuming a basic SQLite database for user storage. Introduction Web applications often handle sensitive user data, such as per