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name: threat-modeling description: Use when implementing auth, file uploads, payments, or external APIs. Applies STRIDE framework systematically. Triggers: "authentication", "file upload", "payment", "multi-tenant", "external API". If thinking "I know security" - use this anyway.

Threat Modeling

MANDATORY FIRST STEP

TodoWrite: Create 18+ items (6 STRIDE categories × 3 items each)

• Define assets/entry points
• Enumerate threats per STRIDE category
• Risk scoring
• Identify controls
• Document threat model
• Verification checkpoint

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Quick-Start Templates

Authentication Feature

Assets: User credentials, session tokens, reset tokens Entry points: Login, signup, password reset endpoints

STRIDE Focus:

Threat	Check
Spoofing	Credential stuffing protection? Rate limiting?
Tampering	Token manipulation? Secure cookies?
Repudiation	Login attempt logging?
Info Disclosure	Token leakage? Error messages reveal info?
DoS	Rate limiting? Account lockout?
EoP	Session hijacking? Privilege escalation?

File Upload Feature

Assets: Stored files, file metadata, server filesystem Entry points: Upload endpoint, file retrieval

STRIDE Focus:

Threat	Check
Spoofing	Impersonate uploader?
Tampering	Malicious files? Path traversal?
Repudiation	Upload logging?
Info Disclosure	Access others' files?
DoS	Large file attacks?
EoP	Execute uploaded code?

Multi-Tenant API

Assets: Tenant data, API endpoints, configurations Entry points: All endpoints with tenant context

STRIDE Focus:

Threat	Check
Info Disclosure	Cross-tenant data leakage?
EoP	Access other tenant's data?
Tampering	Modify tenant_id in requests?
Spoofing	Impersonate other tenant?

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STRIDE Process

Apply each category systematically (S→T→R→I→D→E):

1. Spoofing: Can attacker impersonate?
2. Tampering: Can attacker modify data/code?
3. Repudiation: Can attacker deny actions?
4. Information Disclosure: Can attacker access secrets?
5. Denial of Service: Can attacker disrupt?
6. Elevation of Privilege: Can attacker gain unauthorized access?

Risk Scoring: Likelihood (1-5) × Impact (1-5)

• 15-25: Critical (address immediately)
• 6-14: High (before release)
• 1-5: Low (track)

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Verification Checkpoint

Before marking complete, verify 3 specifics:

1. ✅ Each STRIDE category has ≥2 concrete threats identified
2. ✅ All high-risk (score ≥6) threats have controls documented
3. ✅ Threat model includes data flow diagram with trust boundaries

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Response Templates

"This is over-engineering for a simple feature"

Security bugs cost 30x more post-release than during design. STRIDE takes 15-30 minutes and prevents deployment blockers. Which STRIDE categories don't apply to this feature?

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Red Flags

Thought	Reality
"Ad-hoc brainstorming is faster"	Misses 60% of threats
"Everything is critical"	No risk prioritization = wrong fixes
"We'll security review later"	30x more expensive post-implementation