Threat Model Generation

Generate a comprehensive security threat model for a repository using the STRIDE methodology. This skill analyzes the codebase architecture and produces an LLM-optimized threat model document that other security skills can reference.

When to Use This Skill

• First-time setup - New repository needs initial threat model
• Architecture changes - Significant changes to components, APIs, or data flows
• Security audit - Periodic review or compliance requirement
• Manual request - Security team requests updated threat model

Inputs

Before running this skill, gather or confirm:

Instructions

Follow these steps in order:

Step 1: Analyze Repository Structure

Scan the codebase to understand the system:

1. Identify languages and frameworks

   • Check package.json, requirements.txt, go.mod, Cargo.toml, etc.
   • Note the primary tech stack (e.g., Next.js, Django, Go microservices)

2. Map components and services

   • Look for apps/, services/, packages/ directories
   • Identify entry points: API routes, CLI commands, web handlers
   • Note databases, caches, message queues

3. Identify external interfaces

   • HTTP endpoints (REST, GraphQL)
   • File upload handlers
   • Webhook receivers
   • OAuth/SSO integrations
   • CLI commands that accept user input

4. Trace data flows

   • How does user input enter the system?
   • Where is sensitive data stored?
   • What external services are called?

Step 2: Identify Trust Boundaries

Define security zones:

1. Public Zone (untrusted)

   • All external HTTP endpoints
   • Public APIs without authentication
   • User-uploaded files

2. Authenticated Zone (partially trusted)

   • Endpoints requiring valid session/token
   • User-specific data access
   • Rate-limited APIs

3. Internal Zone (trusted)

   • Service-to-service communication
   • Admin-only endpoints
   • Database connections
   • Secrets management

Document where trust boundaries exist and what validates transitions between zones.

Step 3: Inventory Critical Assets

Classify data by sensitivity:

1. PII (Personally Identifiable Information)

   • User emails, names, addresses, phone numbers
   • Document protection measures

2. Credentials & Secrets

   • Password hashes, API keys, OAuth tokens
   • JWT signing keys, encryption keys
   • Document rotation policies

3. Business-Critical Data

   • Transaction records, customer data
   • Proprietary algorithms, trade secrets
   • Document access controls

Step 4: Apply STRIDE Analysis

For each major component, analyze threats in all six categories:

S - Spoofing Identity

• Can attackers impersonate users or services?
• Are authentication mechanisms secure?
• Look for: weak session handling, API key exposure, missing MFA

T - Tampering with Data

• Can attackers modify data in transit or at rest?
• Look for: SQL injection, XSS, mass assignment, missing input validation

R - Repudiation

• Can users deny actions they performed?
• Look for: missing audit logs, insufficient logging, no immutable trails

I - Information Disclosure

• Can attackers access data they shouldn't?
• Look for: IDOR, verbose errors, hardcoded secrets, data leaks in logs

D - Denial of Service

• Can attackers disrupt service availability?
• Look for: missing rate limits, resource exhaustion, algorithmic complexity

E - Elevation of Privilege

• Can attackers gain unauthorized access levels?
• Look for: missing authorization checks, role manipulation, privilege escalation

For each identified threat:

• Describe the attack scenario
• List vulnerable components
• Show code patterns to look for
• Note existing mitigations
• Identify gaps
• Assign severity (CRITICAL/HIGH/MEDIUM/LOW) and likelihood

Step 5: Document Vulnerability Patterns

Create a library of code patterns specific to this codebase's tech stack:

# Example: SQL Injection patterns for Python
# VULNERABLE
sql = f"SELECT * FROM users WHERE id = {user_id}"

# SAFE
cursor.execute("SELECT * FROM users WHERE id = ?", (user_id,))

Include patterns for:

• SQL injection
• XSS (Cross-Site Scripting)
• Command injection
• Path traversal
• Authentication bypass
• IDOR (Insecure Direct Object Reference)

Step 6: Generate Output Files

Create two files:

1. .factory/threat-model.md

Use the template in stride-template.md to generate a comprehensive threat model with:

• System overview with architecture description
• Trust boundaries and security zones
• Attack surface inventory
• Critical assets classification
• STRIDE threat analysis for each component
• Vulnerability pattern library
• Security testing strategy
• Assumptions and accepted risks
• Version changelog

The document should be written in natural language with code examples, optimized for LLM comprehension.

2. .factory/security-config.json

Generate configuration metadata:

{
  "threat_model_version": "1.0.0",
  "last_updated": "<ISO timestamp>",
  "security_team_contacts": [],
  "compliance_requirements": [],
  "scan_frequency": "on_commit",
  "severity_thresholds": {
    "block_merge": ["CRITICAL"],
    "require_review": ["HIGH", "CRITICAL"],
    "notify_security_team": ["CRITICAL"]
  },
  "vulnerability_patterns": {
    "enabled": [
      "sql_injection",
      "xss",
      "command_injection",
      "path_traversal",
      "auth_bypass",
      "idor"
    ],
    "custom_patterns_path": null
  }
}

Customize based on:

• Detected compliance requirements (from docs, configs, or user input)
• Security team contacts (if provided)
• Tech stack (enable relevant vulnerability patterns)

Success Criteria

The skill is complete when:

• .factory/threat-model.md exists with all sections populated
• .factory/security-config.json exists with valid JSON
• All major components have STRIDE analysis
• Vulnerability patterns match the tech stack
• Document is written in natural language (LLM-readable)
• No placeholder text remains

Verification

Run these checks before completing:

# Verify threat model exists and is non-empty
test -s .factory/threat-model.md && echo "✓ Threat model exists"

# Verify config is valid JSON
cat .factory/security-config.json | jq . > /dev/null && echo "✓ Config is valid JSON"

# Check threat model has key sections
grep -q "## 1. System Overview" .factory/threat-model.md && echo "✓ Has System Overview"
grep -q "## 5. Threat Analysis" .factory/threat-model.md && echo "✓ Has Threat Analysis"
grep -q "## 6. Vulnerability Pattern Library" .factory/threat-model.md && echo "✓ Has Pattern Library"

Example Invocations

Generate initial threat model:

Generate a threat model for this repository using the threat-model-generation skill.

Update existing threat model after architecture change:

Update the threat model - we added a new payments service in services/payments/.

Generate with compliance requirements:

Generate a threat model for this repository. We need to comply with SOC2 and GDPR.

References

• STRIDE Threat Modeling
• OWASP Threat Modeling
• Template: stride-template.md (in this skill directory)