5.5 Threat Modeling and Vulnerability Assessment

What is Threat Modeling?

Threat modeling is a structured process for identifying, analyzing, and prioritizing potential threats to a system before they occur. Teams ask: what are we building, what can go wrong, and what will we do about it? This proactive approach helps developers design defenses early, rather than patching problems after an attack happens.

Identifying Vulnerabilities

A vulnerability assessment systematically scans systems, networks, or applications to find weaknesses — like outdated software, misconfigurations, or weak passwords. Tools generate a report ranking vulnerabilities by severity, helping teams prioritize fixes. This differs from penetration testing, which actively exploits weaknesses rather than just identifying them.

Attack Surface and Trust Boundaries

The attack surface is the sum of all points where an unauthorized user could try to enter or extract data. Trust boundaries mark where data or control passes between components with different privilege levels (e.g., user input entering a server). Reducing attack surface and clearly defining trust boundaries limits opportunities for attackers.

Key terms

Threat modeling

A structured process to identify, analyze, and prioritize potential threats to a system before they are exploited.

Vulnerability assessment

A systematic scan of systems/networks/applications to find and rank weaknesses by severity.

Attack surface

The sum of all points where an unauthorized user could try to enter a system or extract data.

Trust boundary

A point where data or control passes between components with different privilege/trust levels.

Penetration testing vs. vulnerability assessment

Penetration testing actively exploits weaknesses to test defenses; vulnerability assessment only identifies and ranks them.

Try an AP-style question

What is the goal of threat modeling?

1. Find likely threats before attacks
2. Remove all users from a system
3. Write malware for testing
4. Buy the cheapest firewall