IDOR in Cursor-Generated APIs: The Auth Check That Never Shows Up
Cursor and Claude Code generate resource endpoints that authenticate but never verify ownership, allowing any logged-in user to access other users' data.
Why it matters
This vulnerability, known as Insecure Direct Object Reference (IDOR), can lead to serious data breaches if left unaddressed in API implementations.
Key Points
- 1Cursor and Claude Code generate resource endpoints that authenticate but never verify ownership
- 2Any logged-in user can access any other user's data by iterating IDs
- 3Three lines and a helper function can fix the entire pattern across an API
Details
The article discusses a vulnerability in Cursor and Claude Code-generated APIs where resource endpoints authenticate users but do not check if the user actually owns the requested data. This allows any authenticated user to access other users' data by iterating through different IDs. The author discovered this vulnerability while reviewing a friend's SaaS project built using Cursor. The issue stems from the fact that most tutorial code and examples focus on authentication without addressing per-resource ownership checks. AI models like Cursor reproduce these patterns, leading to the same vulnerability across many generated APIs. The article provides a simple three-line fix to address this issue by adding a check to ensure the requested resource belongs to the authenticated user.
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