Attack simulation refers to the ability to simulate attacks targeting both computer networks, systems and applications as well as users and it is more generally referred to breach and attack simulation. While traditional vulnerability scanning technology focuses on the identification of systems, networks and application vulnerabilities, attack simulation tools go the extra mile by allowing to simulate the different phases of the security kill-chain while at the same time providing recommendations on how to secure the organisation. More recently, breach and attack simulation has been focusing more and more on the MITRE ATT&CK knowledge base of adversary tactics and techniques, moving away from the traditional security kill chain model. In the context of cyber ranges, attack simulation is somewhat different from breach and attack simulation solutions, which focus on the delivery of (semi) automatic testing and remediation of a corporate security posture. The main objective of attack simulation within cyber ranges is to add to the realism of the simulation environment with which users interact.