Create API-level tests for non-own property access

test/integration/constructor/_pollution.js

@@ -0,0 +1,98 @@
+/**
+ * @overview Contains helpers to detect non-own property access.
+ * @license MIT
+ */
+
+import assert from "node:assert/strict";
+
+/**
+ * A store for non-own property accesses by proxy.
+ */
+const pollutionState = new Map();
+
+/**
+ * Check whether or not a value is nil (`null` or `undefined`).
+ *
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is nil, `false` otherwise.
+ */
+function isNil(value) {
+  return value === null || value === undefined;
+}
+
+/**
+ * Check whether or not a value is a primitive value.
+ *
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is primitive, `false` otherwise.
+ */
+function isPrimitive(value) {
+  return typeof value === "number" || typeof value === "string";
+}
+
+/**
+ * Check whether or not a value can be wrapped by a `Proxy`.
+ *
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is proxyable, `false` otherwise.
+ */
+function isProxyable(value) {
+  return !(isNil(value) || isPrimitive(value));
+}
+
+/**
+ * Wrap the provided target in in order to monitor it for access to properties
+ * not present on the target.
+ *
+ * @param {any} target The value to wrap.
+ * @returns {any} The wrapped value (or original if wrapping isn't possible).
+ */
+export function wrap(target) {
+  if (!isProxyable(target)) {
+    return target;
+  }
+
+  const nonOwnAccesses = new Set();
+  const proxy = new Proxy(target, {
+    get(target, property, _proxy) {
+      if (!Object.hasOwn(target, property)) {
+        nonOwnAccesses.add(property);
+      }
+
+      // Return normal lookup to ensure normal test execution.
+      return target[property];
+    },
+  });
+
+  pollutionState.set(proxy, nonOwnAccesses);
+  return proxy;
+}
+
+/**
+ * Check if non-own property access was detected on the given wrapped object.
+ *
+ * @param {any} wrapped A `wrap`ped value.
+ * @throws {Error} If non-own property access was detected.
+ */
+export function check(wrapped) {
+  if (!isProxyable(wrapped)) {
+    return;
+  }
+
+  assert.ok(pollutionState.has(wrapped), "target not found");
+  const nonOwnAccesses = pollutionState.get(wrapped);
+
+  // Remove the proxy from the state so re-use of it does not result in errors
+  // from one test to affect other tests. (Also just to reduce memory usage.)
+  pollutionState.delete(wrapped);
+
+  const actual = nonOwnAccesses.size;
+  const expected = 0;
+  const propertiesList = Array.from(nonOwnAccesses.values()).join(", ");
+
+  assert.equal(
+    actual,
+    expected,
+    `Non0own access to ${actual} property(s) detected: ${propertiesList}`,
+  );
+}

test/integration/constructor/constructor.test.js

@@ -3,12 +3,29 @@
  * @license MIT
  */
 
+import { testProp } from "@fast-check/ava";
 import test from "ava";
 
+import * as pollution from "./_pollution.js";
+import { arbitrary } from "../_.js";
+
 import { Shescape } from "shescape";
 
 test("shell is unsupported", (t) => {
   const shell = "not-actually-a-shell-that-exists";
 
   t.throws(() => new Shescape({ shell }), { instanceOf: Error });
 });
+
+testProp(
+  "affected by prototype pollution",
+  [arbitrary.shescapeOptions().map(pollution.wrap)],
+  (t, options) => {
+    try {
+      new Shescape(options);
+    } catch (_) {}
+
+    pollution.check(options);
+    t.pass();
+  },
+);