The combination of high mobility and wireless communication in many safety-critical systems have increased their exposure to malicious security threats. Consequently, many works in the past have proposed solutions to ensure safety and security of these systems. However, not much attention has been given to the interplay between these two groups of nonfunctional requirements. This is a concern as safety solutions may negatively impact system security and vice versa. This paper addresses the interplay between safety and security by proposing an attack injection framework, based on model-implemented fault injection, suitable for model-based design. The framework enables us to study and evaluate the impact of cybersecurity attacks on system safety early in the development process. To this end, we have implemented six attack injection models and conducted experiments on Simulink models of a CAN bus and a brake-by-wire controller. The results show that the security attacks modeled could successfully impact the system safety by violating our defined safety requirements.