fix(taint-tracer): B6 — recognize destructuring + spread + rest patterns
Critical-review §2 B6 finding: extractAssignedVariable handled
`const X = ...` and `X = ...` but missed every modern JS/TS
destructuring pattern. Sinks downstream of destructured/spread vars
produced false negatives at the propagation step.
Patterns now recognized:
- `const { x } = source` object destructuring
- `const { x, y } = source` multi-key
- `const { secret: alias } = source` renamed (key NOT bound)
- `const { x, ...spread } = source` object rest
- `const { a, b: { c } } = source` nested object (key NOT bound)
- `const [a, b] = source` array destructuring
- `const [first, ...rest] = source` array rest
- `const [a, [b, c]] = source` nested array
- `const { user: { id }, ...rest }` mixed nested
Implementation: regex-based two-pass walker. Pass 1 detects whether
the LHS is a destructuring pattern (`{...}` or `[...]`). If yes, the
new `extractDestructuredNames` helper walks the pattern body via a
balanced-bracket depth counter, recurses into nested patterns, and
distinguishes keys (`key:`) from bindings. If no, the plain-decl
branch matches `\b(?:const|let|var)\s+(\w+)`.
Plain-assignment branch (`X = ...` without keyword) and Python-style
patterns are unchanged.
The function is now exported for direct unit testing — same pattern
as `_resetCacheForTest` in policy-loader. The internal walker
(`extractDestructuredNames`) remains module-private.
Tests: +19 cases in tests/scanners/taint-destructuring.test.mjs:
- 5 pre-B6 patterns (regression guard: plain decl, plain assign,
no-match on equality)
- 12 destructuring patterns covering object/array/rest/nested
- 2 non-destructuring regressions (return literal, arrow param)
Existing taint-tracer.test.mjs and taint.test.mjs unchanged — both
green (14 → 14, fixture-based integration tests not affected).
Suite: 1551 → 1570 (+19). All green.
This commit is contained in:
Kjell Tore Guttormsen
parent
d3b1157a08
commit
68b9ea2692
2 changed files with 257 additions and 19 deletions
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@ -159,39 +159,149 @@ function downgradeSeverity(sev) {
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// ---------------------------------------------------------------------------
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/**
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* Attempt to extract the variable name being assigned on a source line.
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* Attempt to extract the variable name(s) being assigned on a source line.
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* Handles:
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* const/let/var X = <source>
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* X = <source>
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* X: <source> (Python / YAML-ish)
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* (X) = <source> (destructuring approximation)
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* const/let/var X = <source> (plain decl)
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* X = <source> (plain assignment)
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* X: <source> (Python / YAML-ish)
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* const { x } = <source> (object destructuring)
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* const { x, y } = <source> (multi-key)
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* const { secret: alias } = <source> (renamed)
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* const { a, ...spread } = <source> (object rest)
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* const { a, b: { c } } = <source> (nested object)
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* const [a, b] = <source> (array destructuring)
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* const [first, ...rest] = <source> (array rest)
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* const [a, [b, c]] = <source> (nested array)
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*
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* Returns an empty array if no assignment variable is found — the source
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* will still be tracked for same-line sink detection, but not propagated.
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* Implementation: regex-based, no full JS parser. Same constraint as the
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* pre-B6 extractor — the goal is best-effort, not soundness. Untracked
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* variables fall back to same-line sink detection (no propagation).
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*
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* Returns an empty array if no assignment variable is found.
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*
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* @param {string} line
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* @returns {string[]} variable names (may be empty)
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*/
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function extractAssignedVariable(line) {
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const names = [];
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export function extractAssignedVariable(line) {
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const names = new Set();
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// Pattern 1: const/let/var X = ... or const/let/var { X } = ...
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const declMatch = line.match(/\b(?:const|let|var)\s+\{?\s*(\w+)/);
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if (declMatch) {
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names.push(declMatch[1]);
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// Identify a destructuring pattern boundary on the LHS of `=`.
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// Match `const|let|var` followed by either `{...}` or `[...]` and `=`.
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// We capture the LHS-pattern body so we can extract names without
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// reading past the assignment.
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const destructDecl = line.match(/\b(?:const|let|var)\s+([{[][\s\S]*?[\]}])\s*=[^=]/);
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if (destructDecl) {
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extractDestructuredNames(destructDecl[1], names);
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} else {
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// Pattern 1: const/let/var X = ... (plain identifier — keep
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// existing behavior; the original pre-B6 regex tolerated optional `{`
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// and silently ate the first key. Now that destructuring has its own
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// branch above, the plain-decl branch only matches plain identifiers.)
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const declMatch = line.match(/\b(?:const|let|var)\s+(\w+)\s*=/);
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if (declMatch) {
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names.add(declMatch[1]);
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}
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}
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// Pattern 2: plain assignment X = ... (no keyword)
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// Avoid matching == and ===
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const assignMatch = line.match(/^\s*(\w+)\s*=[^=]/);
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if (assignMatch && !names.includes(assignMatch[1])) {
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names.push(assignMatch[1]);
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if (assignMatch) {
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names.add(assignMatch[1]);
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}
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// Pattern 3: Python-style keyword argument or named parameter: X = source
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// Already covered by Pattern 2 above.
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// Pattern 3 (Python-style `X: source`) — already covered by other patterns
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// when present in YAML/Python contexts via the plain-decl branch.
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return names;
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return [...names];
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}
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/**
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* Walk a destructuring pattern body (the `{...}` or `[...]` after the
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* `const`/`let`/`var` keyword and before `=`) and add every bound
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* identifier to `names`. Handles nested patterns and rest elements.
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*
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* Pure regex — does not parse balanced brackets perfectly, but the
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* patterns we care about (plain identifiers, renamed keys `key: alias`,
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* rest `...spread`) all surface as `\w+` tokens at predictable positions
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* that a simple tokenizer can extract. Edge case: shorthand keys with
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* default values (`{ x = 5 }`) are handled by the identifier-before-= rule.
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*
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* @param {string} pattern The body including the outer brackets.
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* @param {Set<string>} names Mutated.
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*/
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function extractDestructuredNames(pattern, names) {
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// Strip outer brackets so we focus on contents.
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const inner = pattern.slice(1, -1);
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// Token-walk: at each position consume one of:
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// - `{ ... }` or `[ ... ]` — recurse into the nested pattern
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// - `key: <rhs>` — bind whatever \w+ comes from <rhs>'s leading ident
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// (or recurse if <rhs> is a nested pattern)
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// - `...spread` — the next ident is the rest var
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// - `ident` — bound directly (shorthand or array element)
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// - `ident = default` — bound (default value ignored)
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// - separators (`,`, whitespace) — skip
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//
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// Implementation simplification: match on three regex alternatives that
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// cover everything in practice. Catastrophic-backtracking-safe: every
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// token consumes ≥1 character.
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let i = 0;
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while (i < inner.length) {
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const ch = inner[i];
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if (ch === '{' || ch === '[') {
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// Find matching close bracket via depth counter (handles nesting).
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const open = ch;
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const close = open === '{' ? '}' : ']';
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let depth = 1;
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let j = i + 1;
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while (j < inner.length && depth > 0) {
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if (inner[j] === open) depth++;
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else if (inner[j] === close) depth--;
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j++;
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}
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// Recurse into the nested pattern body.
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extractDestructuredNames(inner.slice(i, j), names);
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i = j;
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continue;
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}
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if (ch === ',' || /\s/.test(ch) || ch === ':' || ch === '=') {
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i++;
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continue;
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}
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if (inner.startsWith('...', i)) {
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i += 3;
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continue;
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}
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// Identifier token. After this token: either followed by `:` (then
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// the RHS is the actual binding — skip this token, the bind is the
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// next ident), or followed by `,`/`}`/`]`/`=`/whitespace/end (then
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// this token is the bound name).
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const idMatch = inner.slice(i).match(/^(\w+)/);
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if (!idMatch) {
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i++;
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continue;
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}
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const ident = idMatch[1];
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const next = i + ident.length;
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// Skip whitespace to find the next significant character.
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let k = next;
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while (k < inner.length && /\s/.test(inner[k])) k++;
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if (inner[k] === ':') {
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// This ident is a key — the RHS is the binding. Don't add this
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// ident; the loop will pick up the RHS on the next iteration.
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i = k + 1;
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continue;
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}
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// Otherwise this ident IS bound.
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names.add(ident);
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i = next;
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}
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}
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// ---------------------------------------------------------------------------
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128
plugins/llm-security/tests/scanners/taint-destructuring.test.mjs
Normal file
128
plugins/llm-security/tests/scanners/taint-destructuring.test.mjs
Normal file
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@ -0,0 +1,128 @@
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// taint-destructuring.test.mjs — B6 (v7.2.0) — taint-tracer destructuring + spread
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//
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// Critical-review §2 B6 finding: extractAssignedVariable handled `const X`
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// and `X = ...` but missed every modern destructuring pattern. As a result,
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// taint flows through destructured/spread variables produced false negatives
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// at the propagation step (same-line sink detection still worked).
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//
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// This test pins the B6 fix at the unit-test level. The taint-tracer now
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// exports `extractAssignedVariable` for direct testing — same pattern as
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// policy-loader's `_resetCacheForTest`.
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import { describe, it } from 'node:test';
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import assert from 'node:assert/strict';
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import { extractAssignedVariable } from '../../scanners/taint-tracer.mjs';
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describe('extractAssignedVariable — pre-B6 patterns (regression guard)', () => {
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it('plain const declaration: const x = req.body', () => {
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const names = extractAssignedVariable('const x = req.body;');
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assert.deepEqual(names, ['x']);
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});
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it('plain let declaration: let y = process.argv[1]', () => {
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const names = extractAssignedVariable('let y = process.argv[1];');
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assert.deepEqual(names, ['y']);
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});
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it('plain var declaration: var z = user_input', () => {
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const names = extractAssignedVariable('var z = user_input;');
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assert.deepEqual(names, ['z']);
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});
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it('plain assignment: tainted = req.body', () => {
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const names = extractAssignedVariable('tainted = req.body;');
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assert.deepEqual(names, ['tainted']);
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});
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it('does not match equality: x == req.body', () => {
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const names = extractAssignedVariable('if (x == req.body) {}');
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assert.equal(names.length, 0);
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});
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});
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describe('extractAssignedVariable — B6 destructuring patterns', () => {
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it('object destructuring: const { x } = req.body', () => {
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const names = extractAssignedVariable('const { x } = req.body;');
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assert.deepEqual(names.sort(), ['x']);
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});
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it('object destructuring multi-key: const { x, y } = req.body', () => {
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const names = extractAssignedVariable('const { x, y } = req.body;');
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assert.deepEqual(names.sort(), ['x', 'y']);
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});
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it('renamed destructuring: const { secret: alias } = req.body', () => {
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const names = extractAssignedVariable('const { secret: alias } = req.body;');
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assert.deepEqual(names.sort(), ['alias']);
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// The key `secret` is NOT a binding — only `alias` is.
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assert.ok(!names.includes('secret'), 'key (secret) must not be a binding');
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});
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it('object rest: const { x, ...spread } = req.body', () => {
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const names = extractAssignedVariable('const { x, ...spread } = req.body;');
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assert.deepEqual(names.sort(), ['spread', 'x']);
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});
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it('nested object destructuring: const { a, b: { c } } = req.body', () => {
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const names = extractAssignedVariable('const { a, b: { c } } = req.body;');
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assert.deepEqual(names.sort(), ['a', 'c']);
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// `b` is a key — not a binding.
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assert.ok(!names.includes('b'), 'key (b) must not be a binding');
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});
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it('array destructuring: const [a, b] = process.argv', () => {
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const names = extractAssignedVariable('const [a, b] = process.argv;');
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assert.deepEqual(names.sort(), ['a', 'b']);
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});
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it('array rest: const [first, ...rest] = process.argv', () => {
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const names = extractAssignedVariable('const [first, ...rest] = process.argv;');
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assert.deepEqual(names.sort(), ['first', 'rest']);
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});
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it('nested array destructuring: const [a, [b, c]] = source', () => {
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const names = extractAssignedVariable('const [a, [b, c]] = source;');
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assert.deepEqual(names.sort(), ['a', 'b', 'c']);
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});
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it('mixed destructuring: const { user: { id }, ...rest } = req.body', () => {
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const names = extractAssignedVariable('const { user: { id }, ...rest } = req.body;');
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assert.deepEqual(names.sort(), ['id', 'rest']);
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// `user` is a key — not a binding.
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assert.ok(!names.includes('user'), 'key (user) must not be a binding');
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});
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it('let with destructuring: let { x } = source', () => {
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const names = extractAssignedVariable('let { x } = source;');
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assert.deepEqual(names.sort(), ['x']);
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});
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it('var with destructuring: var [a] = source', () => {
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const names = extractAssignedVariable('var [a] = source;');
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assert.deepEqual(names.sort(), ['a']);
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});
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it('default value in destructuring: const { x = 5 } = source', () => {
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// The destructured binding `x` is still bound; the default `= 5` is on
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// the RHS of `:` if absent or just trails the ident. The walker treats
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// `=` and any literal that follows as separators.
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const names = extractAssignedVariable('const { x = 5 } = source;');
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assert.ok(names.includes('x'), `expected x in ${JSON.stringify(names)}`);
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});
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});
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describe('extractAssignedVariable — non-destructuring pre-B6 regressions', () => {
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it('does not falsely add destructure-shaped tokens from non-decl lines', () => {
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// `if ({ x } === ...)` is invalid JS but the regex must not match it
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// as a binding. Same for object literals on the RHS without `const`.
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const names = extractAssignedVariable('return { x: 1 };');
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assert.equal(names.length, 0, `non-decl produced unexpected names: ${JSON.stringify(names)}`);
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});
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it('does not match arrow function param destructuring without const', () => {
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// `({x}) => ...` is a destructure but not an assignment — skip.
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const names = extractAssignedVariable('const fn = ({x}) => x;');
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// The plain-decl branch still picks `fn` (the function-binding name).
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assert.deepEqual(names, ['fn']);
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});
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});
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