No industrial operation is free of risk, and different industrial enterprises may legitimately have different “appetites” for certain types of risks. Evaluating cyber risk in industrial control system (ICS) networks is difficult, considering their complex nature. For example, an evaluation can consider explicitly or implicitly up to hundreds of millions of branches of a complex attack tree modelling attack interactions with cyber, physical, safety and protection equipment and processes. This paper was written to assist cyber professionals to understand and communicate the results of such risk assessments to non-technical business decision-makers.
This paper proposes that cyber risk be communicated as a Design Basis Threat (DBT) line drawn through a representative “Top 20” set of cyber attacks. These Top 20 attacks are selected to represent cyber threats to industrial sites across a wide range of circumstances, consequences and sophistication. Many industrial cyber risk practitioners will find the list useful as-is, while expert practitioners may choose to adapt the list to their more detailed understanding of their own sites’ circumstances.
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