Towards a Threat Modeling Approach Addressing Security and Safety in OT Environments

In Industry 4.0, Information Technology (IT) and Operational Technology (OT) tend to converge further with an increasing interdependence of safety and security issues to be considered. On one hand, cyber attacks are possible which can alter implemented safety functionality leading to situations where people are harmed, serious injuries may occur or the environment gets damaged. On the other side, safety can also impact security. For instance, the misuse of a Safety Instrumented System (SIS) may force a machine or a production line to shut down resulting in a denial of service. To prevent or mitigate risks from such scenarios, this paper proposes a threat modeling technique which addresses an integrated view on safety and security. The approach is tailored to the industrial automation domain considering plausible attacks and evaluating risks based on three different metrics. The metrics selected consist of Common Vulnerability Scoring System (CVSS) used as an international standard for rating cyber security vulnerabilities, Security Level (SL) from IEC 62443 to rate cyber security risks in OT environments w.r.t. the underlying architecture, and Safety Integrity Level (SIL) from IEC 61508 to rate safety risks. Due to the variety of use cases involving the chosen metrics, the approach is also feasible for followup analyses, such as integrated safety and security assessments or audits.