vm2

What is vm2?

The vm2 npm package is a sandbox that can run untrusted code with whitelisted built-in modules securely. It provides a secure alternative to the default 'vm' module that comes with Node.js and offers more fine-grained control over what the executed code can do.

What are vm2's main functionalities?

Running Untrusted Code Securely

This feature allows you to execute untrusted JavaScript code in a secure sandbox environment, preventing it from accessing the local system or the host process.

const { NodeVM } = require('vm2');
const vm = new NodeVM();
let result = vm.run('return process.platform;');

Isolation of Modules

With vm2, you can control which modules the sandboxed code can require, either by whitelisting specific modules or by allowing/disallowing external modules.

const { NodeVM } = require('vm2');
const vm = new NodeVM({
  require: {
    external: true
  }
});
vm.run('const fs = require("fs");');

Customizable Sandbox

This feature allows you to create a customizable sandbox with specific global properties that the executed code can interact with.

const { VM } = require('vm2');
const sandbox = { x: 20 };
const vm = new VM({ sandbox });
vm.run('x += 3;');
console.log(sandbox.x); // 23

Hooking Console Methods

vm2 allows you to redirect console methods from the sandboxed code to the host environment, enabling you to hook and handle logs, errors, and other console outputs.

const { NodeVM } = require('vm2');
const vm = new NodeVM({
  console: 'redirect'
});
vm.on('console.log', (data) => {
  console.log('Sandboxed log:', data);
});
vm.run('console.log("Hello from the sandbox!");');

Other packages similar to vm2

sandboxed-module

The 'sandboxed-module' package is similar to vm2 in that it allows for the execution of code in a sandboxed environment. However, it focuses more on requiring modules in a sandbox rather than executing arbitrary code. It does not provide as strong isolation as vm2.

secure-vm

The 'secure-vm' package is another alternative that provides a sandbox for executing code. It is similar to vm2 but has a different API and may not offer the same level of customization and security features as vm2.

README

vm2

vm2 is a sandbox that can run untrusted code with whitelisted Node's built-in modules. Securely!

Features

• Runs untrusted code securely in a single process with your code side by side
• Full control over sandbox's console output
• Sandbox has limited access to process's methods
• Sandbox can require modules (builtin and external)
• You can limit access to certain (or all) builtin modules
• You can securely call methods and exchange data and callbacks between sandboxes
• Is immune to while (true) {} (see docs)
• Is immune to all known methods of attacks
• Transpilers support

How does it work

• It uses internal VM module to create secure context
• It uses Proxies to prevent escaping the sandbox
• It overrides builtin require to control access to modules

What is the difference between Node's vm and vm2?

Try it yourself:

const vm = require('vm');
vm.runInNewContext('this.constructor.constructor("return process")().exit()');
console.log('Never gets executed.');

const {VM} = require('vm2');
new VM().run('this.constructor.constructor("return process")().exit()');

Installation

IMPORTANT: Requires Node.js 6 or newer.

npm install vm2

Quick Example

const {VM} = require('vm2');
const vm = new VM();

vm.run(`process.exit()`); // TypeError: process.exit is not a function

const {NodeVM} = require('vm2');
const vm = new NodeVM({
	require: {
		external: true
	}
});

vm.run(`
	var request = require('request');
	request('http://www.google.com', function (error, response, body) {
		console.error(error);
		if (!error && response.statusCode == 200) {
			console.log(body) // Show the HTML for the Google homepage.
		}
	})
`, 'vm.js');

Documentation

• VM
• NodeVM
• VMScript
• Error handling
• Read-only objects
• Cross-sandbox relationships
• CLI
• 2.x to 3.x changes
• 1.x and 2.x docs
• Contributing

VM

VM is a simple sandbox, without require feature, to synchronously run an untrusted code. Only JavaScript built-in objects + Buffer are available.

Options:

• timeout - Script timeout in milliseconds.
• sandbox - VM's global object.
• compiler - javascript (default) or coffeescript or custom compiler function.

IMPORTANT: Timeout is only effective on code you run through run. Timeout is NOT effective on any method returned by VM.

const {VM} = require('vm2');

const vm = new VM({
    timeout: 1000,
    sandbox: {}
});

vm.run("process.exit()"); // throws ReferenceError: process is not defined

You can also retrieve values from VM.

let number = vm.run("1337"); // returns 1337

TIP: See tests for more usage examples.

NodeVM

Unlike VM, NodeVM lets you require modules same way like in regular Node's context.

Options:

• console - inherit to enable console, redirect to redirect to events, off to disable console (default: inherit).
• sandbox - VM's global object.
• compiler - javascript (default) or coffeescript or custom compiler function.
• require - true or object to enable require method (default: false).
• require.external - true to enable require of external modules (default: false).
• require.builtin - Array of allowed builtin modules (default: none).
• require.root - Restricted path where local modules can be required (default: every path).
• require.mock - Collection of mock modules (both external or builtin).
• require.context - host (default) to require modules in host and proxy them to sandbox. sandbox to load, compile and require modules in sandbox. Builtin modules except events always required in host and proxied to sandbox.
• require.import - Array of modules to be loaded into NodeVM on start.
• nesting - true to enable VMs nesting (default: false).
• wrapper - commonjs (default) to wrap script into CommonJS wrapper, none to retrieve value returned by the script.

IMPORTANT: Timeout is not effective for NodeVM so it is not immune to while (true) {} or similar evil.

REMEMBER: The more modules you allow, the more fragile your sandbox becomes.

const {NodeVM} = require('vm2');

const vm = new NodeVM({
	console: 'inherit',
    sandbox: {},
    require: {
        external: true,
        builtin: ['fs', 'path'],
        root: "./",
        mock: {
	        fs: {
		        readFileSync() { return 'Nice try!'; }
	        }
        }
    }
});

// Sync

let functionInSandbox = vm.run("module.exports = function(who) { console.log('hello '+ who); }");
functionInSandbox('world');

// Async

let functionWithCallbackInSandbox = vm.run("module.exports = function(who, callback) { callback('hello '+ who); }");
functionWithCallbackInSandbox('world', (greeting) => {
	console.log(greeting);
});

When wrapper is set to none, NodeVM behaves more like VM for synchronous code.

assert.ok(vm.run('return true') === true);

TIP: See tests for more usage examples.

Loading modules by relative path

To load modules by relative path, you must pass full path of the script you're running as a second argument of vm's run method. Filename then also shows up in any stack traces produced from the script.

vm.run("require('foobar')", "/data/myvmscript.js");

VMScript

You can increase performance by using pre-compiled scripts. The pre-compiled VMScript can be run later multiple times. It is important to note that the code is not bound to any VM (context); rather, it is bound before each run, just for that run.

const {VM, VMScript} = require('vm2');

const vm = new VM();
const script = new VMScript("Math.random()");
console.log(vm.run(script));
console.log(vm.run(script));

Works for both VM and NodeVM.

const {NodeVM, VMScript} = require('vm2');

const vm = new NodeVM();
const script = new VMScript("module.exports = Math.random()");
console.log(vm.run(script));
console.log(vm.run(script));

Code is compiled automatically first time you run it. You can compile the code anytime with script.compile(). Once the code is compiled, the method has no effect.

Error handling

Errors in code compilation and synchronous code execution can be handled by try/catch. Errors in asynchronous code execution can be handled by attaching uncaughtException event handler to Node's process.

try {
	var script = new VMScript("Math.random()").compile();
} catch (err) {
	console.error('Failed to compile script.', err);
}

try {
	vm.run(script);
} catch (err) {
	console.error('Failed to execute script.', err);
}

process.on('uncaughtException', (err) => {
	console.error('Asynchronous error caught.', err);
})

Read-only objects

To prevent sandboxed script to add/change/delete properties to/from the proxied objects, you can use VM.freeze/NodeVM.freeze methods to make the object read-only. Rather than freezing the object itself (like builtin Object.freeze method does) it creates a new proxy so the original object remains untouched.

Example without using VM.freeze:

const util = {
	add: (a, b) => a + b
}

const vm = new VM({
	sandbox: {util}
});

vm.run('util.add = (a, b) => a - b');
console.log(util.add(1, 1)); // returns 0

Example with using VM.freeze:

const vm = new VM({
	sandbox: {util: VM.freeze(util)}
});

vm.run('util.add = (a, b) => a - b'); // throws Object is read-only.

Cross-sandbox relationships

const assert = require('assert');
const {VM} = require('vm2');

const sandbox = {
	object: new Object(),
	func: new Function(),
	buffer: new Buffer([0x01, 0x05])
}

const vm = new VM({sandbox});

assert.ok(vm.run(`object`) === sandbox.object);
assert.ok(vm.run(`object instanceof Object`));
assert.ok(vm.run(`object`) instanceof Object);
assert.ok(vm.run(`object.__proto__ === Object.prototype`));
assert.ok(vm.run(`object`).__proto__ === Object.prototype);

assert.ok(vm.run(`func`) === sandbox.func);
assert.ok(vm.run(`func instanceof Function`));
assert.ok(vm.run(`func`) instanceof Function);
assert.ok(vm.run(`func.__proto__ === Function.prototype`));
assert.ok(vm.run(`func`).__proto__ === Function.prototype);

assert.ok(vm.run(`new func() instanceof func`));
assert.ok(vm.run(`new func()`) instanceof sandbox.func);
assert.ok(vm.run(`new func().__proto__ === func.prototype`));
assert.ok(vm.run(`new func()`).__proto__ === sandbox.func.prototype);

assert.ok(vm.run(`buffer`) === sandbox.buffer);
assert.ok(vm.run(`buffer instanceof Buffer`));
assert.ok(vm.run(`buffer`) instanceof Buffer);
assert.ok(vm.run(`buffer.__proto__ === Buffer.prototype`));
assert.ok(vm.run(`buffer`).__proto__ === Buffer.prototype);
assert.ok(vm.run(`buffer.slice(0, 1) instanceof Buffer`));
assert.ok(vm.run(`buffer.slice(0, 1)`) instanceof Buffer);

CLI

Before you can use vm2 in command line, install it globally with npm install vm2 -g.

$ vm2 ./script.js

Known Issues

• It is not possible to define class that extends proxied class.

Sponsors

Development is sponsored by Integromat.

License

Copyright (c) 2014-2017 Patrik Simek

The MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.