Privilege Escalation in REST APIs
The logs showed normal traffic—until a single endpoint call gained access to data it should never touch. That was privilege escalation.
Privilege escalation in REST APIs happens when a user bypasses access controls and performs actions beyond their authorization. Most cases are due to broken authorization checks, flawed role logic, or unvalidated parameters. Attackers exploit gaps in vertical privileges (jumping to higher roles) and horizontal privileges (accessing other users’ data with the same role).
The risk is amplified in REST APIs because endpoints are often exposed to the public internet. Common vectors include:
- Missing or incorrect role-based access control (RBAC) enforcement.
- Insecure direct object references (IDOR) where endpoint IDs reveal unauthorized resources.
- Failure to validate a user’s ownership against parameters passed in the request.
- Overly broad tokens or scopes in OAuth/OpenID configurations.
Mitigation starts at design. Every endpoint must enforce server-side checks for both authentication and authorization, regardless of how the client presents the request. Never rely on hidden UI elements or client-limited functionality. Implement strict RBAC or ABAC (attribute-based access control), validate IDs against the authenticated user, and minimize token privilege to the least required scope.
Logging and monitoring are not optional. Detect anomalies by watching for unusual access patterns and failed authorization attempts. Automate alerts when a non-admin account calls admin endpoints. Run security testing specifically targeting privilege escalation via REST API calls, including fuzzing parameter values and manipulating headers.
Privilege escalation is not just an API bug. It is a direct handover of power to a hostile actor. Build with denial at every layer, audit relentlessly, and close every gap before it’s exploited.
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