This document discusses insecure direct object references (IDOR), which occur when a developer exposes references like file or database keys without access control. This allows attackers to access unauthorized data by manipulating the references. The document provides examples of IDOR vulnerabilities found in Twitter, Oculus, Square, Zapier, and WordPress. It emphasizes having a generic access control model, using user IDs instead of numeric IDs, and thoroughly reviewing code to prevent IDOR issues.