On the Meaning and Purpose of Attack Trees

Abstract

Attack trees are a popular notation for describing threats to systems, both in academia and industry. Originally, attack trees lacked a formal semantics, but formal semantics for different variants of attack trees were proposed later. These semantics focus on the attacker^{\prime}s actions defined in the leaves and the logical structure defined by the inner nodes of an attack tree. Surprisingly, they do not clarify the connection to the goal defined at the root node in a satisfactory fashion. In this article, we aim at a better clarification of this connection between the attacks and the attacker goal specified by an attack tree. We argue that there are multiple sensible success criteria for attacks wrt. a given attacker goal and develop a framework for defining such criteria. We exploit our framework to identify similarities and differences between automatic attack-tree generation techniques. Finally, we propose a novel variant of attack trees that allows one to express exploits in an explicit fashion.