Threat Model Source Code Repo

Deliver an actionable AppSec-grade threat model that is specific to the repository or a project path, not a generic checklist. Anchor every architectural claim to evidence in the repo and keep assumptions explicit. Prioritizing realistic attacker goals and concrete impacts over generic checklists.

Quick start

• Collect (or infer) inputs:

• Repo root path and any in-scope paths.

• Intended usage, deployment model, internet exposure, and auth expectations (if known).

• Any existing repository summary or architecture spec.

• Use prompts in references/prompt-template.md to generate a repository summary.

• Follow the required output contract in references/prompt-template.md . Use it verbatim when possible.

Workflow

1. Scope and extract the system model

• Identify primary components, data stores, and external integrations from the repo summary.

• Identify how the system runs (server, CLI, library, worker) and its entrypoints.

• Separate runtime behavior from CI/build/dev tooling and from tests/examples.

• Map the in-scope locations to those components and exclude out-of-scope items explicitly.

• Do not claim components, flows, or controls without evidence.

2. Derive boundaries, assets, and entry points

• Enumerate trust boundaries as concrete edges between components, noting protocol, auth, encryption, validation, and rate limiting.

• List assets that drive risk (data, credentials, models, config, compute resources, audit logs).

• Identify entry points (endpoints, upload surfaces, parsers/decoders, job triggers, admin tooling, logging/error sinks).

3. Calibrate assets and attacker capabilities

• List the assets that drive risk (credentials, PII, integrity-critical state, availability-critical components, build artifacts).

• Describe realistic attacker capabilities based on exposure and intended usage.

• Explicitly note non-capabilities to avoid inflated severity.

4. Enumerate threats as abuse paths

• Prefer attacker goals that map to assets and boundaries (exfiltration, privilege escalation, integrity compromise, denial of service).

• Classify each threat and tie it to impacted assets.

• Keep the number of threats small but high quality.

5. Prioritize with explicit likelihood and impact reasoning

• Use qualitative likelihood and impact (low/medium/high) with short justifications.

• Set overall priority (critical/high/medium/low) using likelihood x impact, adjusted for existing controls.

• State which assumptions most influence the ranking.

6. Validate service context and assumptions with the user

• Summarize key assumptions that materially affect threat ranking or scope, then ask the user to confirm or correct them.

• Ask 1–3 targeted questions to resolve missing context (service owner and environment, scale/users, deployment model, authn/authz, internet exposure, data sensitivity, multi-tenancy).

• Pause and wait for user feedback before producing the final report.

• If the user declines or can’t answer, state which assumptions remain and how they influence priority.

7. Recommend mitigations and focus paths

• Distinguish existing mitigations (with evidence) from recommended mitigations.

• Tie mitigations to concrete locations (component, boundary, or entry point) and control types (authZ checks, input validation, schema enforcement, sandboxing, rate limits, secrets isolation, audit logging).

• Prefer specific implementation hints over generic advice (e.g., "enforce schema at gateway for upload payloads" vs "validate inputs").

• Base recommendations on validated user context; if assumptions remain unresolved, mark recommendations as conditional.

8. Run a quality check before finalizing

• Confirm all discovered entrypoints are covered.

• Confirm each trust boundary is represented in threats.

• Confirm runtime vs CI/dev separation.

• Confirm user clarifications (or explicit non-responses) are reflected.

• Confirm assumptions and open questions are explicit.

• Confirm that the format of the report matches closely the required output format defined in prompt template: references/prompt-template.md

• Write the final Markdown to a file named <repo-or-dir-name>-threat-model.md (use the basename of the repo root, or the in-scope directory if you were asked to model a subpath).

Risk prioritization guidance (illustrative, not exhaustive)

• High: pre-auth RCE, auth bypass, cross-tenant access, sensitive data exfiltration, key or token theft, model or config integrity compromise, sandbox escape.

• Medium: targeted DoS of critical components, partial data exposure, rate-limit bypass with measurable impact, log/metrics poisoning that affects detection.

• Low: low-sensitivity info leaks, noisy DoS with easy mitigation, issues requiring unlikely preconditions.

References

• Output contract and full prompt template: references/prompt-template.md

• Optional controls/asset list: references/security-controls-and-assets.md

Only load the reference files you need. Keep the final result concise, grounded, and reviewable.

When to Use

When NOT to Use