Towards Interdependent Safety Security Assessments using Bowties

TL;DR

This paper proposes a unified approach using Bowtie Diagrams to assess the interdependencies between safety and security, demonstrated through a case study of Facebook's DNS outage.

Contribution

It introduces a method to combine safety and security assessments into a single Bowtie model, capturing their interdependencies.

Findings

Unified safety-security assessment model using Bowties

Application to Facebook DNS outage case study

Insights into safety-security barrier interactions

Abstract

We present a way to combine security and safety assessments using Bowtie Diagrams. Bowties model both the causes leading up to a central failure event and consequences which arise from that event, as well as barriers which impede events. Bowties have previously been used separately for security and safety assessments, but we suggest that a unified treatment in a single model can elegantly capture safety-security interdependencies of several kinds. We showcase our approach with the example of the October 2021 Facebook DNS shutdown, examining the chains of events and the interplay between the security and safety barriers which caused the outage.