Input: "User registration API that accepts email, password, stores in database"

Output:

THREAT MODEL: User Registration API

TRUST BOUNDARIES:
- Client ↔ API Server
- API Server ↔ Database

STRIDE ANALYSIS:
[S] Spoofing: Weak password policy, no email verification
[T] Tampering: SQL injection in email field, password storage without hashing
[R] Repudiation: No registration audit logs
[I] Information Disclosure: Error messages leak user existence
[D] Denial of Service: No rate limiting on registration attempts
[E] Elevation of Privilege: Default user roles not restricted

TOP 3 RISKS:
1. HIGH: SQL injection → Database compromise
2. MEDIUM: Weak passwords → Account takeover
3. MEDIUM: No rate limiting → Resource exhaustion

MITIGATIONS:
- Input validation and parameterized queries
- Strong password policy + hashing (bcrypt/Argon2)
- Rate limiting (5 attempts/minute per IP)

Progress:

• Map data flow and trust boundaries
• Apply STRIDE to each boundary crossing
• Prioritize threats by likelihood × impact
• Define specific mitigations
• Review against OWASP Top 10

Step 1: Parse Feature Scope Extract: data types, user roles, external dependencies, storage

Step 2: Identify Trust Boundaries Map where data crosses security contexts (user→app, app→database, app→external service)

Step 3: Apply STRIDE Framework For each boundary:

• Spoofing: Can attacker impersonate legitimate entity?
• Tampering: Can data be modified maliciously?
• Repudiation: Can actions be denied later?
• Information Disclosure: Can sensitive data leak?
• Denial of Service: Can availability be impacted?
• Elevation of Privilege: Can permissions be bypassed?

Step 4: Risk Prioritization

• HIGH: Easy to exploit + severe impact
• MEDIUM: Moderate effort or impact
• LOW: Difficult to exploit + minimal impact

Example 1: Input: File upload endpoint for profile pictures Output:

BOUNDARIES: Client → Upload Handler → File Storage
THREATS:
[T] Malicious file upload (executable disguised as image)
[D] Large file DOS attack
[I] Directory traversal in filename
MITIGATIONS: File type validation, size limits, sandboxed storage

Example 2: Input: Payment processing integration with Stripe Output:

BOUNDARIES: Frontend → Backend → Stripe API
THREATS:
[S] API key exposure in client code
[T] Amount manipulation before Stripe call
[I] Payment data logged in plaintext
MITIGATIONS: Server-side validation, PCI-compliant logging, key rotation