What is the purpose of Threat Modeling diagrams and what do they visualize?

They overlay trust boundaries onto a data-flow diagram (processes, flows, stores, external entities) so you can apply STRIDE wherever data crosses from one trust level to another.

* Threat-model DFD — STRIDE is applied where a data flow crosses the dashed trust boundary into the trusted server zone. *

Threat Model Components:

• Processes - Components that process data
• Data Flows - Movement of data between components
• Data Stores - Where data is stored
• Trust Boundaries - Lines separating different trust levels (shown as dashed red lines)
• External Entities - Users, attackers, external systems

Trust Boundary Analysis:

• Data crossing trust boundaries requires special attention
• Different colored zones indicate different trust/risk levels:
  • Yellow/Orange: Lower trust zones
  • Pink/Red: Higher risk zones
  • Green: Trusted/secure zones

STRIDE Application:

• Apply STRIDE to each element crossing trust boundaries
• Identify threats at each data flow
• Document threats with red markers/indicators

Key Insight: Threat modeling combines DFDs with trust boundaries to systematically identify where security controls are needed.

Go deeper:

• OWASP Threat Modeling Cheat Sheet — DFDs, trust boundaries, and applying STRIDE where data crosses boundaries.