What is an IDOR Bug?

Insecure Direct Object References (IDOR) occur when an application provides direct access to objects based on user-supplied input. If access control checks are missing, an attacker can modify the input parameter to point to an object they shouldn't have access to. In simpler terms, if a user can change a number in a URL parameter from id=101 to id=102 and view another user’s private invoice, medical record, or profile draft, the application suffers from an IDOR vulnerability.

IDOR Risks in e-Commerce and Membership Sites

In WordPress, IDOR bugs are highly prevalent in WooCommerce extensions, learning management systems (LMS), and membership plugins. These systems handle thousands of unique database rows representing sensitive customer objects. If a developer assumes that a user will only click links generated by the UI, they might skip checking if the user actually owns the requested resource. Attackers scan these endpoints, shifting ID numbers sequentially to harvest private customer data.

Remediation Strategies for IDOR

Preventing IDOR relies on strict ownership verification before any object data is returned or modified:

  • Implement Ownership Verification: Never trust that the user has the right to view an object just because they know its ID. Always query the database to verify that the current_user_id matches the user ID associated with the requested object.

  • Use Indirect Object References: Instead of exposing internal database IDs (like 1, 2, 3), map resources to temporary, session-specific tokens or random Universally Unique Identifiers (UUIDs).

  • Enforce Strict Parameter Type Checking: Ensure parameters are cast to their expected types, and reject inputs that deviate from the expected structure.