In this paper we present an attack injection approach for security protocol testing aiming at vulnerability detection. We use attack tree model to describe known attacks and derive injection test scenarios to test the security properties of the protocol under evaluation. The test scenarios are converted to a specific fault injector script after performing some transformations. The attacker is emulated using a fault injector. This model based approach facilitates there usability and maintainability of the generated injection attacks as well as the generation of fault injectors scripts. The approach is applied to an existing mobile security protocol. We performed experiments with truncation and DoS attacks; results show good precision and efficiency in the injection method