AI Coding Tools Like Cursor Often Miss Ownership Checks, Exposing User Data

AI code editors such as Cursor routinely generate API routes that verify a user is logged in but fail to confirm whether that user owns the requested resource, a flaw known as Insecure Direct Object Reference (IDOR, CWE-639). A developer demonstrated the vulnerability by building an invoice endpoint with Cursor, then accessing another user's private invoice simply by changing the ID in the URL. The root cause is that AI models were trained on tutorials that treat authentication and authorization as the same thing, reproducing patterns that stop at login checks and omit object-level access control. The fix requires scoping the database query to the authenticated user's ID, so the database itself never returns records belonging to someone else. Applying this single-query ownership filter in Node.js or Python eliminates the exposure and also avoids leaking whether a record exists at all.