In this paper, we consider a Trust Model with Group Leader (GL)-based communication in VANET. This model is used to classify vehicles based on their trustworthiness and elect potential GLs. We propose a security risk assessment methodology and we apply it to our Trust Model. This methodology is used for identifying threats, assessing the risk involved, and defining approaches to mitigate them. The risk assessment includes assessment of the impact and likelihood of occurrence of attacks relevant to the identified threats, evaluation of the Trust Model design principles, validation of the built-in security, and the mitigation actions of attacks. Based on this assessment, we demonstrated the resiliency of the Trust Model to resist to many security attacks.