nyx/docs/detectors.md

# Detectors

Nyx ships four independent detector families. They run together in `--mode full`, the default. Findings are merged, deduplicated, ranked, and printed in one result set.

| Family | Rule prefix | Looks at | What it finds |
|---|---|---|---|
| [Taint analysis](detectors/taint.md) | `taint-*` | Cross-file dataflow | Unsanitized data flowing source to sink |
| [CFG structural](detectors/cfg.md) | `cfg-*` | Per-function control flow | Auth gaps, unguarded sinks, error fallthrough, resource release on all paths |
| [State model](detectors/state.md) | `state-*` | Per-function state lattice | Use-after-close, double-close, leaks, unauthenticated access |
| [AST patterns](detectors/patterns.md) | `<lang>.<cat>.<name>` | Tree-sitter structural match | Banned APIs, weak crypto, dangerous constructs |

The taint family is split into cap-specific rule classes when a sink callee carries multiple vulnerability classes:

| Rule id | Cap | Surface |
|---|---|---|
| `taint-unsanitised-flow` | every cap except `data_exfil` and `unauthorized_id` | Default taint flow class |
| `taint-data-exfiltration` | `data_exfil` | Sensitive data flowing into the payload of an outbound network request (body / headers / json on `fetch`, body on `XMLHttpRequest.send`). Distinct from SSRF: the destination is fixed but attacker-influenced bytes leave the process. |
| `rs.auth.missing_ownership_check.taint` | `unauthorized_id` | Rust auth subsystem fold-in; see [auth.md](auth.md). |

A single call site can fire several of these at once when it carries multiple gates — `fetch(taintedUrl, {body: tainted})` produces both an SSRF finding (URL flow) and a `taint-data-exfiltration` finding (body flow), each with its own cap mask rather than a conflated union.

For Rust auth-specific rules (`rs.auth.*`), see [auth.md](auth.md).

## How they combine

In `--mode full`:

1. **Taint and AST can both fire on one line.** If `eval(userInput)` triggers both `js.code_exec.eval` (AST) and `taint-unsanitised-flow` (taint), both are kept with distinct rule IDs. The taint finding ranks higher because of the analysis-kind bonus.
2. **State supersedes CFG on resource leaks.** When `state-resource-leak` and `cfg-resource-leak` fire at the same location, the CFG one is dropped.
3. **Exact duplicates are removed.** Same line, column, rule ID, severity → one finding.

## Modes

| Mode | Active detectors |
|---|---|
| `full` (default) | All four |
| `ast` | AST patterns only |
| `cfg` | Taint + CFG + State (no AST patterns) |
| `taint` | Taint + State |

## Attack-surface ranking

Every finding gets a deterministic score. Findings are sorted by descending score by default. Disable with `--no-rank` or `output.attack_surface_ranking = false`.

```
score = severity_base + analysis_kind + evidence_strength + state_bonus - validation_penalty
```

| Component | Values |
|---|---|
| Severity base | High=60, Medium=30, Low=10 |
| Analysis kind | taint=+10, state=+8, cfg with evidence=+5, cfg without evidence=+3, ast=+0 |
| Evidence strength | +1 per evidence item up to 4; +2 to +6 for source kind |
| State bonus | use-after-close / unauthed=+6, double-close=+3, must-leak=+2, may-leak=+1 |
| Validation penalty | -5 if path-validated |

Source-kind contributions (taint only):

| Source | Bonus |
|---|---|
| User input (`req.body`, `argv`, `stdin`, `form`, `query`, `params`) | +6 |
| Environment (`env::var`, `getenv`, `process.env`) | +5 |
| Unknown | +4 |
| File system | +3 |
| Database | +2 |

Approximate score ranges:

| Finding type | Score |
|---|---|
| High taint with user input | 76 to 81 |
| High state (use-after-close) | ~74 |
| High CFG structural | 63 to 68 |
| Medium taint with env source | 45 to 50 |
| Medium state (resource leak) | ~40 |
| Low AST-only pattern | ~10 |

For the engine's runtime model (passes, summaries, SCC fixed-point), see [how-it-works.md](how-it-works.md).