Introduction to Threat Modeling

In the rapidly evolving landscape of cybersecurity, reacting to threats is no longer enough. Threat Modeling is a proactive approach that helps you identify, understand, and communicate threats and mitigations within the context of protecting something of value.

What is Threat Modeling?

Threat modeling is a structured process with these objectives:

1. Identify security requirements.
2. Pinpoint security threats and potential vulnerabilities.
3. Quantify threat and vulnerability criticality.
4. Prioritize remediation methods.

The 4 Question Framework

Adam Shostack, a leading expert in the field, proposes four key questions to guide the threat modeling process:

1. What are we building? (System Diagrams, Data Flow Diagrams)
2. What can go wrong? (Threat Identification)
3. What are we going to do about it? (Mitigation Strategy)
4. Did we do a good job? (Validation and Retrospective)

Example Threat Model (PlantUML)

Here is a simple Data Flow Diagram (DFD) visualizing a threat model for a web application:

STRIDE Methodology

One of the most common methodologies for identifying threats ("What can go wrong?") is STRIDE, developed by Microsoft.

Threat	Security Property Violated	Definition
Spoofing	Authenticity	Pretending to be something or someone other than yourself.
Tampering	Integrity	Modifying something on disk, network, memory, or elsewhere.
Repudiation	Non-repudiation	Claiming that you didn't do something or were not responsible.
Information Disclosure	Confidentiality	Providing information to someone not authorized to see it.
Denial of Service	Availability	Absorbing resources needed to provide service.
Elevation of Privilege	Authorization	Allowing someone to do something they are not authorized to do.

Why Start Now?

Integrating threat modeling into your SDLC (Software Development Life Cycle) reduces the cost of fixing vulnerabilities. Fixing a security bug during the design phase is significantly cheaper than fixing it in production.

"Security is a process, not a product." - Bruce Schneier

Conclusion

Threat modeling doesn't have to be complicated. Start small, diagram your key flows, and ask "What can go wrong?". Your users (and your future self) will thank you.