The vulnerability stems from the order of operations in REST request processing. In annotation-based security scenarios, the JSON deserialization occurs before security checks due to:
- Resteasy Reactive's handler chain executing parameter extraction (including JSON deserialization) in ResourceMethodInvokerHandler
- Security interceptors being applied later in the chain
This violates the security-first principle, allowing potential deserialization attacks even when the request should be rejected by authorization checks. The functions identified are core to the deserialization and request handling workflow in Resteasy Reactive, and their execution order relative to security checks makes them vulnerable.