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A Hybrid Threat Modeling Method

March 2018 Technical Note
Nancy R. Mead, Forrest Shull, Krishnamurthy Vemuru (University of Virginia), Ole Villadsen (Carnegie Mellon University)

Presents a hybrid method of threat modeling that attempts to meld the desirable features of three methods: Security Cards, Persona non Grata, and STRIDE.

Publisher:

Software Engineering Institute

CMU/SEI Report Number

CMU/SEI-2018-TN-002

Abstract

In FY 2016, the research team evaluated Security Cards, STRIDE (Spoofing identity, Tampering with data, Repudiation, Information disclosure, Denial of service, Elevation of privilege), and persona non grata (PnG) for effectiveness in threat identification. Security Cards is an approach that emphasizes creativity and brainstorming over more structured approaches such as checklists. STRIDE involves modeling a system and subsystem and related data flows. PnGs represent archetypal users who behave in unwanted, possibly nefarious ways. The team used two scenarios: an aircraft maintenance scenario and a drone swarm scenario, both described in this technical note in detail, along with the project outcomes. No individual threat modeling method included all identified threats.

The research team subsequently developed the Hybrid Threat Modeling Method (hTMM), considering the desirable characteristics for a Threat Modeling Method. At a high level, the hTMM includes the following steps, described in detail in the technical note: (1) Identify the system you will be threat modeling. (2) Apply Security Cards according to developers’ suggestions. (3) Prune PnGs that are unlikely or for which no
realistic attack vectors could be identified. (4) Summarize results from the above steps, utilizing tool support. (5) Continue with a formal risk assessment method.