Abstract: In one aspect, a distributed security-testing infrastructure is used for attack-tree modeling for penetration testing. An API framework, fully distributed and scalable, is used to access the attack-tree modeling based on attack trees, or decision trees, to emulate attacker behavior and decisions taken during an attack. The API framework allows developers to implement the security tools into existing software to perform actions based on desired conditions as defined by the nodes of the attack tree. For example, APIs can be used along with if/else-type statements to create advanced threat models that react based on given conditions to test multiple paths through the attack tree. Nodes of the attack tree are configured to perform actions based on the output of previous attacks in other nodes. This flexible design allows for the easy modification of the threat modeling system to test new scenarios.