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willianbswillianbs/skills/threat-modeler/SKILL.md

threat-modeler

Skill0 starsChanged 4 months agoMITView on GitHub

Builds asset- and STRIDE-based threat models before deep security audits. Use for new features touching auth, data, trust boundaries, or HighRisk specs. Emits THREAT_MODEL. Never invents exploits or replaces security-auditor findings.

8 other projects use a version of this.

Adopted by

Most recently taken up by

The file

We split this skill into the rules it gives an agent

3 rules. 0 are common, 3 are distinctive, and 0 are very specific to this project.

  • 0

    Common

    Most of the 8 edited versions we read keep these.

  • 3

    Distinctive

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Never invent vulnerabilities in code you did not reason about.

    line 95
  2. Distinctive:

    Never replace security-auditor with a shallow STRIDE table alone for ship decisions.

    line 97
  3. Distinctive:

    Never skip assets/boundaries and jump to OWASP laundry lists.

    line 98

“Common” is measured: kept by at least 6 in 10 of the 8 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Purpose

Produce a structured threat model (assets, trust boundaries, STRIDE abuse cases, prioritized threats) that security-auditor and delivery-planner can consume.

When to Use / When NOT to Use

Use when: new HighRisk features; auth/PII/payments/integrations; before security-auditor on greenfield surfaces; architecture changes that move trust boundaries.

Do not use when: style-only PRs; trivial chores; full vuln hunting (security-auditor); active exploit response without modeling first is OK to skip lite.

Preconditions

Scope (feature/system) and enough CONTEXT_PACK to identify actors, data, and boundaries. If missing, ask before inventing assets.

Inputs / Outputs

Inputs: feature/system scope, CONTEXT_PACK, SPEC_STATUS (preferred), data classification if known.

Outputs: THREAT_MODEL

Upstream / Downstream

Upstream: context-loader, spec-validator, delivery-planner, engineering-os.

Downstream: security-auditor, delivery-planner, adr-enforcer, test-strategy-designer.

Core Principles

  1. Assets and trust boundaries before checklists.
  2. STRIDE-light: Spoofing, Tampering, Repudiation, Info disclosure, DoS, Elevation.
  3. Threats need actor + asset + abuse path.
  4. Prioritize by Likelihood × Impact; mark assumptions.
  5. Feed security-auditor — do not duplicate deep code audit.
  6. Redact secrets; never invent CVEs.
  7. Unknown boundaries → ProceedWithConditions, not fake completeness.

Process

Lite

Single feature / small API: list assets, 2–4 trust boundaries, top STRIDE threats, hand off.

Full

  1. Actors — users, admins, services, attackers, insiders.
  2. Assets — data, secrets, sessions, money, admin actions, reputation.
  3. Diagram (textual) — components and trust boundaries.
  4. STRIDE pass per boundary/asset.
  5. Threat list — ID, description, likelihood, impact, severity, mitigations (existing vs needed).
  6. Out of scope — explicitly list.
  7. Decision: Proceed to security-auditor / Revise design / Block if Critical unmitigated design flaw.

Evidence Requirements

Cite real modules/APIs from CONTEXT_PACK. Label assumptions. No invented endpoints.

Stop Conditions / Failure Modes

ConditionAction
Cannot identify assets/boundariesAsk; Block if HighRisk
Design has Critical unmitigated threatBlock until design change or accepted risk
Scope is pure UI copyRefuse; not applicable

Severity + Confidence

Threat severity uses portfolio standard. Critical = auth bypass / mass data exposure / RCE-class design flaws.

Output Contract

## THREAT_MODEL
Scope: ...
Actors: ...
Assets: ...
Trust boundaries: ...
Threats:
  - ID, STRIDE, severity, likelihood, impact, mitigations
Assumptions: ...
Decision: Proceed | ProceedWithConditions | Revise | Block

Handoffs

security-auditor (primary), adr-enforcer (security architecture), test-strategy-designer (negative cases), delivery-planner (mitigation tasks).

Never

  • Never invent vulnerabilities in code you did not reason about.
  • Never print secrets.
  • Never replace security-auditor with a shallow STRIDE table alone for ship decisions.
  • Never skip assets/boundaries and jump to OWASP laundry lists.

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