Threat Modeling
Identify and mitigate security threats during system design.
When to Use This Skill
Use this skill when:
- Designing a new system, service, or feature
- Making significant architectural changes to existing systems
- Onboarding a new third-party integration or dependency
- Preparing for security audits or compliance reviews
- Responding to a security incident to improve defenses
- Reviewing infrastructure changes that affect trust boundaries
Prerequisites
- System architecture documentation or design diagrams
- Access to development and operations teams for context
- Understanding of the system's data classification (PII, PHI, financial, etc.)
- OWASP Threat Dragon or Microsoft Threat Modeling Tool (optional but helpful)
- Whiteboard or diagramming tool for collaborative sessions
STRIDE Methodology
| Threat | Description | Property Violated | Mitigation Examples |
|---|
| Spoofing | Pretending to be another user or system | Authentication | MFA, mTLS, API key validation, certificate pinning |
| Tampering | Modifying data in transit or at rest | Integrity | HMAC, digital signatures, checksums, immutable logs |
| Repudiation | Denying having performed an action | Non-repudiation | Audit logging, digital signatures, tamper-evident logs |
| Information Disclosure | Exposing data to unauthorized parties | Confidentiality | Encryption (TLS, AES), access controls, data masking |
| Denial of Service | Making service unavailable | Availability | Rate limiting, autoscaling, CDN, circuit breakers |
| Elevation of Privilege | Gaining unauthorized higher access | Authorization | RBAC, principle of least privilege, input validation |
STRIDE Worksheet Template
# stride-worksheet.yaml - Fill out one per component/trust boundary crossing
component:
name: "API Gateway"
owner: "Platform Team"
data_classification: "Confidential"
trust_boundary: "External -> Internal"
threats:
- id: T001
category: Spoofing
description: "Attacker forges JWT tokens to impersonate users"
attack_vector: "Stolen signing key or weak algorithm (HS256 with guessable secret)"
likelihood: Medium
impact: Critical
risk_score: 15 # likelihood(3) x impact(5)
existing_controls:
- "JWT validation on every request"
- "RS256 algorithm with rotated keys"
gaps:
- "No token binding to device/IP"
recommended_mitigations:
- "Add token binding claims"
- "Implement short-lived tokens (15 min) with refresh"
- "Monitor for token reuse from different IPs"
status: "Mitigated (partial)"
owner: "Auth Team"
- id: T002
category: Tampering
description: "Man-in-the-middle modifies API requests"
attack_vector: "Compromised network between client and gateway"
likelihood: Low
impact: High
risk_score: 8
existing_controls:
- "TLS 1.3 enforced"
- "HSTS enabled"
gaps: []
recommended_mitigations:
- "Certificate pinning for mobile clients"
status: "Mitigated"
owner: "Platform Team"
- id: T003
category: Information Disclosure
description: "Verbose error messages leak internal details"
attack_vector: "Triggering errors returns stack traces, internal IPs, DB schema"
likelihood: High
impact: Medium
risk_score: 12
existing_controls:
- "Generic error pages in production"
gaps:
- "Some microservices return raw exceptions"
recommended_mitigations:
- "Centralized error handling middleware"
- "Error response schema validation"
status: "Open"
owner: "Backend Team"
- id: T004
category: Denial of Service
description: "API rate limiting bypass through distributed requests"
attack_vector: "Botnet sending requests below per-IP threshold"
likelihood: Medium
impact: High
risk_score: 12
existing_controls:
- "Per-IP rate limiting at WAF"
gaps:
- "No aggregate rate limiting"
- "No bot detection"
recommended_mitigations:
- "Add aggregate rate limiting per endpoint"
- "Deploy bot detection (Cloudflare Bot Management)"
- "Implement circuit breaker pattern"
status: "Open"
owner: "Platform Team"
- id: T005
category: Elevation of Privilege
description: "IDOR allows accessing other users' data"
attack_vector: "Manipulating resource IDs in API calls"
likelihood: Medium
impact: Critical
risk_score: 15
existing_controls:
- "Authentication required"
gaps:
- "Authorization checks inconsistent across endpoints"
recommended_mitigations:
- "Enforce ownership checks on all resource access"
- "Use opaque IDs instead of sequential integers"
- "Add authorization integration tests"
status: "Open"
owner: "Backend Team"
Data Flow Diagram
Text-Based DFD Notation
Trust Boundary: Internet
==========================
|
[External User]
|
HTTPS/443
|
==========================
Trust Boundary: DMZ
==========================
|
(WAF / CDN)
|
[API Gateway]---->[Auth Service]--->[Identity DB]
|
==========================
Trust Boundary: Internal
==========================
|
[App Service]
/ \
/ \
[Cache] [Message Queue]
|
[Worker Service]
|
==========================
Trust Boundary: Data
==========================
|
[Primary DB]--->[Replica DB]
|
[Object Store]
Legend:
[Box] = Process
(Parens) = External entity / proxy
==== = Trust boundary
---> = Data flow
Threat Dragon Model (JSON)
{
"summary": {
"title": "E-Commerce Platform",
"owner": "Security Team",
"description": "Threat model for the e-commerce API platform"
},
"detail": {
"diagrams": [
{
"title": "API Data Flow",
"diagramType": "STRIDE",
"cells": [
{
"type": "tm.Actor",
"name": "Web Client",
"threats": []
},
{
"type": "tm.Process",
"name": "API Gateway",
"threats": ["T001", "T002", "T003", "T004"]
},
{
"type": "tm.Process",
"name": "Order Service",
"threats": ["T005"]
},
{
"type": "tm.Store",
"name": "Orders Database",
"threats": ["T006"]
},
{
"type": "tm.Boundary",
"name": "DMZ"
},
{
"type": "tm.Boundary",
"name": "Internal Network"
}
]
}
]
}
}
Threat Library
# threat-library.yaml - Reusable threat patterns
categories:
authentication:
- id: TL-AUTH-001
name: "Credential stuffing"
description: "Attacker uses leaked credential databases to attempt logins"
applicable_to: ["login endpoints", "API authentication"]
mitigations: ["MFA", "rate limiting", "credential breach monitoring", "CAPTCHA"]
- id: TL-AUTH-002
name: "Session hijacking"
description: "Attacker steals session tokens via XSS or network sniffing"
applicable_to: ["web applications", "APIs with session tokens"]
mitigations: ["HttpOnly cookies", "TLS", "session binding", "short TTL"]
- id: TL-AUTH-003
name: "OAuth token theft"
description: "Access tokens stolen from logs, URLs, or insecure storage"
applicable_to: ["OAuth/OIDC integrations"]
mitigations: ["PKCE", "short-lived tokens", "token binding", "secure storage"]
injection:
- id: TL-INJ-001
name: "SQL injection"
description: "Malicious SQL in user input executes unauthorized queries"
applicable_to: ["database-backed endpoints", "search functionality"]
mitigations: ["parameterized queries", "ORM", "input validation", "WAF"]
- id: TL-INJ-002
name: "Command injection"
description: "User input passed to system commands without sanitization"
applicable_to: ["file processing", "system administration features"]
mitigations: ["avoid shell commands", "input allowlisting", "sandboxing"]
- id: TL-INJ-003
name: "SSRF (Server-Side Request Forgery)"
description: "Attacker makes server send requests to internal resources"
applicable_to: ["URL fetching features", "webhook handlers", "PDF generators"]
mitigations: ["URL allowlisting", "network segmentation", "metadata endpoint blocking"]
supply_chain:
- id: TL-SC-001
name: "Dependency confusion"
description: "Malicious package with internal name published to public registry"
applicable_to: ["npm, pip, maven projects using private packages"]
mitigations: ["namespace scoping", "registry prioritization", "SBOM monitoring"]
- id: TL-SC-002
name: "Compromised CI/CD pipeline"
description: "Attacker injects malicious code through build system compromise"
applicable_to: ["all software builds"]
mitigations: ["SLSA compliance", "signed commits", "ephemeral builders", "provenance"]
data:
- id: TL-DATA-001
name: "Unencrypted data at rest"
description: "Sensitive data stored without encryption on disk or in database"
applicable_to: ["databases", "object storage", "backups"]
mitigations: ["AES-256 encryption", "KMS-managed keys", "encrypted volumes"]
- id: TL-DATA-002
name: "PII exposure in logs"
description: "Personal data written to application or infrastructure logs"
applicable_to: ["all services handling PII"]
mitigations: ["log sanitization", "structured logging", "PII detection scanning"]
Risk Scoring Matrix
Likelihood Rating
| Score | Level | Description |
|---|
| 1 | Very Low | Requires nation-state resources; no known exploits |
| 2 | Low | Requires significant expertise and specific conditions |
| 3 | Medium | Moderately skilled attacker with available tools |
| 4 | High | Script-kiddie level; public exploits available |
| 5 | Very High | Trivial to exploit; automated scanning detects it |
Impact Rating
| Score | Level | Description |
|---|
| 1 | Negligible | No data exposure; cosmetic only |
| 2 | Minor | Limited data exposure; single user affected |
| 3 | Moderate | Significant data exposure; service degradation |
| 4 | Major | Large-scale data breach; extended outage |
| 5 | Critical | Complete system compromise; regulatory breach |
Risk Matrix
Impact -> 1 2 3 4 5
Likelihood
5 Medium High High Critical Critical
4 Low Medium High High Critical
3 Low Low Medium High High
2 Info Low Low Medium High
1 Info Info Low Low Medium
Risk Treatment Decisions
risk_treatment:
critical: # Score >= 20
action: "Immediate remediation required"
sla: "24 hours"
approval: "CISO"
high: # Score 12-19
action: "Remediation in current sprint"
sla: "1 week"
approval: "Security Lead"
medium: # Score 6-11
action: "Remediation in next sprint"
sla: "1 month"
approval: "Team Lead"
low: # Score 2-5
action: "Track and address in backlog"
sla: "1 quarter"
approval: "Team Lead"
info: # Score 1
action: "Accept risk and document"
sla: "None"
approval: "Team Lead"
OWASP Threat Dragon Setup
# Run Threat Dragon locally with Docker
docker run -d \
--name threat-dragon \
-p 3000:3000 \
-e ENCRYPTION_KEYS='["threat-dragon-encryption-key-change-me"]' \
-e NODE_ENV=production \
owasp/threat-dragon:v2.2.0
# Access at http://localhost:3000
# Or install as desktop application
# Download from: https://github.com/OWASP/threat-dragon/releases
Integration with CI/CD
# .github/workflows/threat-model-review.yml
name: Threat Model Review
on:
pull_request:
paths:
- 'docs/threat-model/**'
- 'architecture/**'
jobs:
validate:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- name: Validate threat model files
run: |
for model in docs/threat-model/*.yaml; do
echo "Validating $model..."
python -c "
import yaml, sys
with open('$model') as f:
data = yaml.safe_load(f)
required = ['component', 'threats']
for r in required:
if r not in data:
print(f'ERROR: Missing required field: {r}')
sys.exit(1)
for t in data.get('threats', []):
if t.get('status') == 'Open' and t.get('risk_score', 0) >= 12:
print(f'WARNING: High-risk open threat: {t[\"id\"]} - {t[\"description\"]}')
print(f'OK: {len(data[\"threats\"])} threats documented')
"
done
- name: Check for unaddressed critical threats
run: |
CRITICAL=$(grep -r "risk_score: \(1[5-9]\|2[0-5]\)" docs/threat-model/*.yaml | grep "status: \"Open\"" | wc -l)
if [ "$CRITICAL" -gt 0 ]; then
echo "WARNING: $CRITICAL critical/high-risk threats still open"
echo "Review required before merging architectural changes"
fi
Troubleshooting
| Problem | Cause | Solution |
|---|
| Threat model sessions are unproductive | Participants don't understand the system | Share architecture docs before the session; include a system walkthrough |
| Too many threats identified | Scope too broad | Focus on one component or trust boundary per session |
| Threats are too vague | No structured methodology | Use STRIDE per element; fill in the worksheet template for each |
| Team doesn't follow up on findings | No ownership or tracking | Assign each threat to a team with SLA; track in issue tracker |
| Threat model becomes stale | No trigger to update | Require review on architecture changes (CI/CD gate on diagram changes) |
| Disagreements on risk scores | Subjective scoring | Use the scoring matrix consistently; calibrate with historical incidents |
Best Practices
- Integrate threat modeling into the SDLC at the design phase
- Review threat models when architecture changes occur
- Include developers, ops, and security in sessions
- Use the threat library to ensure consistent coverage
- Document all risk acceptance decisions with rationale
- Track threats in the same system as other work items
- Conduct annual reviews of all active threat models
- Start with the most critical data flows and expand
- Keep sessions timeboxed (90 minutes maximum)
- Maintain a living threat library updated with new patterns
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