Insecure Direct Object References (IDOR) are a class of access control vulnerability where an application exposes a direct reference to an internal implementation object, such as a database key or file name, without proper authorization checks. Attackers can exploit this by simply changing the identifier in a request to access or modify resources belonging to other users. This issue is particularly prevalent in RESTful APIs where resource IDs are often sequential and predictable.
Detection typically involves manual testing with multiple user accounts, automated scanning tools that fuzz object IDs, and thorough code review of authorization logic. Common tools include Burp Suite, OWASP ZAP, and custom scripts that compare responses across different user contexts. The impact of IDOR can range from data leakage to full account takeover, making it a high-priority finding in security assessments.
Mitigation strategies include implementing robust object-level authorization checks, using unpredictable identifiers (e.g., UUIDs), and enforcing server-side validation of user permissions for every resource access. Regular security testing and adopting a zero-trust model for API design are critical to preventing these flaws. As APIs continue to proliferate, IDOR remains a top concern for security teams worldwide.