thedixitjain Threat Model — Attack Surface Analysis
Iron Law
Every system has an attack surface. If you haven't identified it, you haven't secured it.
Process
Step 0: Load Engagement Context
Check for .harness/engagement.md in the project root. If present, load the scope (in-scope/out-of-scope) and constraints. Skip threat modeling for explicitly out-of-scope components.
Without engagement context, proceed with full-surface analysis.
Step 1: Identify Trust Boundaries
Map every boundary where data crosses a trust level:
- External → Internal: API endpoints, webhooks, file uploads, user input
- Internal → Privileged: DB queries, file system access, shell execution
- Service → Service: Inter-service communication, message queues, shared state
- Client → Server: Auth tokens, session state, CORS origins
For each boundary, document:
- Data flow direction
- Input validation present (yes/no/partial)
- Authentication required (yes/no)
- Encryption in transit (yes/no)
Step 2: Enumerate Threat Actors
| Actor | Motivation | Capability | Target |
|---|---|---|---|
| Anonymous user | Exploration | Low | Public endpoints |
| Authenticated user | Data access | Medium | Own data + IDOR targets |
| Malicious insider | Data exfiltration | High | All internal systems |
| Compromised dependency | Supply chain | Variable | Build/deploy pipeline |
Step 3: Generate Threat Scenarios
For each trust boundary × threat actor combination, generate:
- Attack vector: How the boundary is crossed maliciously
- Impact: What is compromised (CIA triad — Confidentiality, Integrity, Availability)
- Likelihood: High/Medium/Low based on exposure and complexity
- Existing mitigations: What already prevents this
- Gap: What is missing
Step 4: Produce Output
Write THREAT_MODEL.md:
# Threat Model — {project}
## Scope
- In-scope: {from engagement.md or full codebase}
- Out-of-scope: {from engagement.md or none}
- Date: {ISO date}
## Trust Boundaries
| # | Boundary | Direction | Validation | Auth | Encryption |
|---|----------|-----------|------------|------|------------|
| 1 | ... | ... | ... | ... | ... |
## Threat Scenarios
| ID | Boundary | Actor | Vector | Impact | Likelihood | Mitigated | Gap |
|----|----------|-------|--------|--------|------------|-----------|-----|
| T1 | ... | ... | ... | ... | ... | Partial | ... |
## Priority Remediation
1. [CRITICAL] {highest risk gap}
2. [HIGH] {next gap}
3. [MEDIUM] {remaining gaps}
## Assumptions
- {list all assumptions made during analysis}
Step 5: Feed into vuln-scan
After producing the threat model, suggest:
"Run /vuln-scan to validate threat scenarios against the codebase."
Anti-Rationalization
| Excuse | Rebuttal | What to do instead |
|---|---|---|
| "We don't have any external-facing components" | Internal trust boundaries are attack surfaces too. Lateral movement starts inside. | Model internal boundaries with the same rigor. |
| "Threat modeling is overkill for a small project" | Small projects get breached too. The model is proportional to the codebase. | Run the process. It takes 10 minutes. A breach takes months. |
| "We already have a threat model" | Threat models expire. Every code change can invalidate assumptions. | Update the model when significant changes land. |
| "The framework handles security" | Frameworks don't model YOUR business logic threats. | Add application-layer threat scenarios on top of framework defaults. |
Evidence Required
- Every trust boundary in the codebase identified
- At least 2 threat scenarios per boundary
- Each scenario has impact, likelihood, and gap assessment
- Priority remediation list ordered by risk
- Assumptions explicitly listed (not hidden)
Red Flags
- Skipping boundaries because they're "internal"
- Listing only one threat scenario per boundary
- Marking all scenarios as "already mitigated" without evidence
- No assumptions section — means assumptions are hidden, not absent
- Threat model that doesn't reference actual code paths
Source: hashgraph-online/awesome-codex-plugins → plugins/epicsagas/epic-harness/skills/threat-model/SKILL.md