Open_Ultra_SAST/docs/threat-model.md

# Threat model & hardening

OpenUltraSAST analyzes **untrusted code**. This document states what it trusts, what
it does not, and the controls that keep a scan safe to run in CI and safe to share.

## Trust boundaries

- **Scanned code is untrusted input.** Quick and standard modes never import, build or run
  the target: quick reads source as text, and standard additionally parses it into a code
  property graph with Joern (`joern-parse`, a parser, not a build) and may send code excerpts
  to the configured model. Only `deep` mode executes target-derived code: its REGRESS stage
  loads promoted candidates inside the Docker sandbox below, and it runs only when `docker
  info` succeeds (otherwise the stage is skipped and recorded as `sandbox_unavailable`).
- **The ruleset and CWE policy are trusted, governed data.** They change only through
  reviewed commits or the bounded self-improvement loop (`ousast improve`), which can
  flip rule *status* and tune score constants but can never edit pattern text or the
  authoritative 0–5 severity. See [architecture.md](architecture.md#self-improvement).
- **Provider credentials are the operator's.** The core install (PyYAML only) makes no
  network calls on its own. A local scan calls a model only in standard or deep mode, and
  only when a key is available: the model layer asks the residual question the graph cannot
  settle, and `[models] hunter` enables the tool hunter. LLM calls go to DeepSeek
  (`DEEPSEEK_API_KEY`); OpenRouter (`OPENROUTER_API_KEY`) serves embeddings. Keys come from
  the environment or a gitignored `.env`, which never overrides an exported variable. The
  pre-push check calls a model only with an explicit `--model-config`. Agentic work runs on the plane (`ousast plane run`): `ousast` reads
  the variable a task's Model names (`secretKey.key`) from the operator's environment or
  `.env` and sends the key only in that task's start request, through Agent Substrate's
  router to that task's actor. It is not baked into an image or task template, and it is
  never logged or written to artifacts.

## Controls

### Secret redaction
Scan artifacts can quote source that contains live credentials. `redaction.py` masks
recognizable secret shapes (provider API keys, AWS/GitHub/Slack/Google tokens, bearer
tokens, URL-embedded credentials, PEM private keys, and `key = value` assignments for
sensitive names) before traces (`trace/events.jsonl`) and the markdown report are
written. On by default; disable with `[hardening] redact_secrets = false`.

### Plane egress
Each plane task runs in its own actor behind Agent Substrate's egress gateway, which
denies by default. The task's EgressPolicy (`src/openultrasast/plane/egress.py`) allows exactly three
things: plain HTTP to the artifact receiver, and TLS passthrough to the Git hosts of the
task's bound Workspaces and to the hosts its bound Model declares
(`openultrasast.io/egress-hosts`). There are no wildcards, no IP addresses and no TLS
interception. The policy is deleted with the actor.

### Cost & CI budgets
- **Agentic spend** is bounded per plane task by the Run's `budget: {usd, calls}`. The
  metered client refuses the next call once either ceiling is reached (the task is
  `unfinished` and resumes on a rerun with a larger budget). A usd budget on a Model
  without prices is refused rather than metered as zero, and an account or
  authentication error fails the task and starts nothing further. The standard-mode tool
  hunter is bounded by the per-tier hunter budgets.
- **Output size** is bounded by `[hardening] max_findings` (0 = unlimited). Truncation is
  severity-ordered and disclosed as a `budget` degradation in the manifest.

### Provider reliability
LLM/embedding calls retry transient failures (HTTP 429/5xx, connection errors, timeouts)
with exponential backoff; non-transient errors (e.g. 4xx, malformed JSON) fail fast.

### Visible degradation & determinism
When an optional capability is missing (Joern, Docker, a model, a provider key), the scan
falls back to its deterministic equivalent and records a `degradations` entry in the
manifest — it is never silently downgraded. Runs are reproducible: fixed config,
artifact manifests, prompt hashes, and model identifiers are recorded.

### MCP surface
`ousast mcp` exposes only the ten narrow project tools. No tool runs arbitrary shell,
Docker, or internal hunter tools, and no tool accepts a free-form command argument.

## Sandbox (deep mode)

The REGRESS stage (`regress/`, `sandbox/runner.py`) runs each snippet with `docker run`
and never mounts the host Docker socket:

| Control | Setting |
|---|---|
| network | `--network none`, always; a host-network argument is refused |
| source | the target bind-mounted read-only at `/workspace`; root filesystem `--read-only` |
| scratch | a tmpfs at `/scratch` for the snippet |
| user | non-root `65534:65534`, `--cap-drop ALL`, `no-new-privileges` |
| memory | `[sandbox] memory_mb`, default 2048 MB |
| pids | `[sandbox] pids_limit`, default 512 |
| timeout | `[sandbox] timeout_seconds`, default 300 s |

Before anything runs, a structural deny-list (`regress/safety.py`) rejects a snippet that
mentions sockets, curl, host networking or writes under `/workspace`.