Threat Model (A06:2025)

What this checks

This skill produces the threat-model context a developer needs before writing the code: what is this thing, where will it run, what inputs do we trust, what inputs do we not. It does not emit findings or apply a checklist of "missing controls" — that's the developer's job once they have the context.

Single source of truth: this skill delegates to the threat-modeling subagent in .claude/agents/threat-modeling.md. The subagent's JSON output is the canonical threat-model shape.

Vulnerable patterns

This is an orchestrator skill. The agent it dispatches has no vulnerable-pattern catalog of its own — it produces context, and later auditors (vulnerability-audit, design-review, contract-audit) use that context to find code-level issues.

Procedure

Use the Agent tool to dispatch one threat-modeling subagent. Pass it the plan, spec, or codebase under discussion. The subagent returns a JSON object describing purpose, deployment, trusted inputs, and untrusted inputs.

Render that JSON as a Markdown report for the developer. Do not show the raw JSON. The report shape:

## Threat Model — <one-line summary derived from purpose>

**Purpose.** <purpose>

**Deployment.** <deployment>

**Trusted inputs** (the maintainer controls these; auditors should
not flag content originating here):

- <category 1>
- <category 2>
- ...

**Untrusted inputs** (cross a trust boundary; every one needs an
explicit handling step in the plan — validation, rate limit,
authentication, etc.):

- <category 1>
- <category 2>
- ...

---

*Use this as the design checklist for what your plan must address.
The skill produced context; deciding which controls to add is
yours.*

The closing line is intentional — this skill does not enforce specific controls or emit findings. It surfaces the trust-boundary picture; the developer decides what to add (auth on new endpoints, rate limits on user-facing surface, validation on external-service responses, …).

Verification

• Output is a Markdown report (not raw JSON) with a ## Threat Model heading
• Purpose, Deployment, Trusted inputs, and Untrusted inputs are each present as labeled sections
• Trusted-input and untrusted-input categories are listed explicitly (one bullet per category)
• The report describes the system; it does NOT list "missing controls", recommend specific mitigations, or emit findings — that work belongs to design-review or to the developer's own follow-up

References

• CWE-693 (Protection Mechanism Failure)
• CWE-657 (Violation of Secure Design Principles)
• OWASP A06:2025 Insecure Design