Threat Model Skill for Codex

Security Threat Model

Objective

Establish the repository-scoped threat model at the path defined in ../../references/scan-artifacts.md. Reuse a cached model only when its final Repository and Version lines match the current target.

AGENTS.md or resolved SECURITY.md guidance can be that authoritative source when it is sufficiently specific about the repository's product surfaces, trust boundaries, attacker-controlled inputs, assumptions, or security scan guidance to serve as the threat model.

If no threat model is provided, generate a repository-scoped threat model to be used in future bug discovery. The threat model should holistically cover the entire repository and should make it obvious:

• what assets or privileges matter
• what trust boundaries exist
• what inputs are attacker-controlled
• what invariants the code must preserve
• what repository-wide failure modes would matter most

Artifact Resolution

The path references in this skill are the default locations for this phase.

If the user explicitly provides a different path for a required input or output, use the user-provided path instead of the corresponding default path referenced in this skill.

If a required input is still missing, stop and ask the user for it before continuing.

Use the shared scan artifact path conventions in ../../references/scan-artifacts.md.

Workflow

• Resolve target_id, the current version (revision for an immutable Git tree, snapshot digest otherwise), and the repository-scoped threat model path using ../../references/scan-artifacts.md.
• If the repository-scoped threat model exists, reuse it only when its final Repository and Version lines match those current values. Otherwise regenerate it.
• Before inspecting repository source or generating a threat model, read ../../references/security-guidance.md and the policy resolved for the scan target. Resolve it first if the coordinator did not supply it.
• If a threat model or authoritative security scan guidance is provided or referenced:
• preserve it unchanged as the threat model body
• treat that body as the only threat model source of truth
• do not expand, summarize, or reinterpret the body
• AGENTS.md is acceptable here when it is clearly being used as the security scan guidance or threat model source for this scan and is sufficiently repository-specific to stand in for a threat model
• Otherwise, generate a repository-scoped threat model using the checklist below.
• Before finalizing this phase, sanity-check that:
• the threat model is repository-scoped rather than being centered around any specific scan target
• it describes repository-wide primary product or runtime surfaces and trust boundaries before covering any narrower examples
• any vulnerability-class discussion is about repository-context classes, not findings about any current diff
• Append the exact Repository and Version lines from ../../references/scan-artifacts.md, then write the threat model to the repository-scoped path.

Threat Model Generation Guidance

Generate and structure the threat model using references/threat-model-guidance.md.

Hard Rules

• A provided threat model or authoritative security scan guidance is authoritative. Keep its body unchanged and append only the required cache footer.
• Threat model generation must stay at repository scope unless the user explicitly asks for narrower scope.
• Do not turn this phase into findings about any current diff.
• Do not let the current scan target, touched subsystem, or changed directories become the center of gravity for this phase unless the user explicitly asks for that narrower scope.
• In large monorepos, avoid centering personal/, test/, tests/, docs/, examples/, or one-off developer tooling unless repository evidence shows those are real deployed or privileged workflow surfaces.
• Call out trust boundaries and assumptions explicitly.
• Keep references to vulnerability types at the level of repository-context classes, rather than any diff findings.
• Persist the threat model output to the repository-scoped threat model path from ../../references/scan-artifacts.md.