From 5b9187ed674a060cd70b8cc7fe584a70ec38ff65 Mon Sep 17 00:00:00 2001
From: Chengzhong Wu <cwu631@bloomberg.net>
Date: Fri, 27 Mar 2026 10:31:53 -0400
Subject: [PATCH] vm: `DONT_CONTEXTIFY` when no contextObject set

When `contextObject` is not passed in `vm.createContext`, do not
contextify by default. This reduces the chance that the script semantics
are broken by the interceptors.
---
 lib/vm.js                                     |  2 +-
 ...est-vm-function-declaration-uses-define.js |  2 +-
 test/parallel/test-vm-strict-define.js        | 51 +++++++++++++++++++
 3 files changed, 53 insertions(+), 2 deletions(-)
 create mode 100644 test/parallel/test-vm-strict-define.js

diff --git a/lib/vm.js b/lib/vm.js
index ae710806201893..c3c76f6d6a2700 100644
--- a/lib/vm.js
+++ b/lib/vm.js
@@ -222,7 +222,7 @@ function getContextOptions(options) {
 }
 
 let defaultContextNameIndex = 1;
-function createContext(contextObject = {}, options = kEmptyObject) {
+function createContext(contextObject = vm_context_no_contextify, options = kEmptyObject) {
   if (contextObject !== vm_context_no_contextify && isContext(contextObject)) {
     return contextObject;
   }
diff --git a/test/known_issues/test-vm-function-declaration-uses-define.js b/test/known_issues/test-vm-function-declaration-uses-define.js
index 1cfdd9c368e570..a7f7aa92e78d4a 100644
--- a/test/known_issues/test-vm-function-declaration-uses-define.js
+++ b/test/known_issues/test-vm-function-declaration-uses-define.js
@@ -9,7 +9,7 @@ const common = require('../common');
 const vm = require('vm');
 const assert = require('assert');
 
-const ctx = vm.createContext();
+const ctx = vm.createContext({});
 Object.defineProperty(ctx, 'x', {
   enumerable: true,
   configurable: true,
diff --git a/test/parallel/test-vm-strict-define.js b/test/parallel/test-vm-strict-define.js
new file mode 100644
index 00000000000000..4c14f1f73d2f7a
--- /dev/null
+++ b/test/parallel/test-vm-strict-define.js
@@ -0,0 +1,51 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+
+const vm = require('vm');
+
+// Declared with `var`.
+{
+  const ctx = vm.createContext();
+  vm.runInContext(`"use strict"; var x; x = 42;`, ctx);
+  assert.strictEqual(ctx.x, 42);
+}
+
+// Define on `globalThis`.
+{
+  const ctx = vm.createContext();
+  vm.runInContext(`
+    "use strict";
+    Object.defineProperty(globalThis, "x", {
+      configurable: true,
+      value: 42,
+    });
+  `, ctx);
+  const ret = vm.runInContext(`"use strict"; x`, ctx);
+  assert.strictEqual(ret, 42);
+  assert.strictEqual(ctx.x, 42);
+}
+
+// Set on globalThis.
+{
+  const ctx = vm.createContext();
+  vm.runInContext(`"use strict"; globalThis.x = 42`, ctx);
+  const ret = vm.runInContext(`"use strict"; x`, ctx);
+  assert.strictEqual(ret, 42);
+  assert.strictEqual(ctx.x, 42);
+}
+
+// Set on context.
+// Should throw a ReferenceError when a variable is not defined in strict-mode.
+assert.throws(() => vm.runInNewContext(`"use strict"; x = 42`),
+              /ReferenceError: x is not defined/);
+
+// Known issue since V8 14.6.
+// When the context is a "contextified" object, ReferenceError can not be thrown.
+// TODO(legendecas): https://github.com/nodejs/node/pull/61898#issuecomment-4142811603
+// Refs: https://chromium-review.googlesource.com/c/v8/v8/+/7474608
+{
+  const ctx = vm.createContext({});
+  assert.throws(() => vm.runInContext(`"use strict"; x = 42`, ctx),
+                /ReferenceError: x is not defined/);
+}