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vm2
![Known Vulnerabilities](https://snyk.io/test/github/patriksimek/vm2/badge.svg)
‼️ Project Discontinued ‼️
TL;DR The library contains critical security issues and should not be used for production! The maintenance of the project has been discontinued. Consider migrating your code to isolated-vm.
Dear community,
It's been a truly remarkable journey for me since the vm2 project started nine years ago. The original intent was to devise a method for running untrusted code in Node, with a keen focus on maintaining in-process performance. Proxies, an emerging feature in JavaScript at that time, became our tool of choice for this task.
From the get-go, we recognized the arduous task that lay ahead, as we tried to safeguard against the myriad of escape scenarios JavaScript presented. However, the thrill of the chase kept us going, hopeful that we could overcome these hurdles.
Through the years, this project has seen numerous contributions from passionate individuals. I wish to extend my deepest gratitude to all of you. Special thanks go to @XmiliaH, whose unwavering dedication in maintaining and improving this library over the last 4 years was instrumental to its sustained relevance.
Unfortunately, the growing complexity of Node has brought us to a crossroads. We now find ourselves facing an escape so complicated that fixing it seems impossible. And this isn't about one isolated issue. Recent reports have highlighted that sustaining this project in its current form is not viable in the long term.
Therefore, we must announce the discontinuation of this project.
You may wonder, "What now?"
While this may seem like an end, I see it as an opportunity for you to transition your projects and adapt to a new solution. We would recommend migrating your code to the isolated-vm, a library which employs a slightly different, yet equally effective, approach to sandboxing untrusted code.
Thank you all for your support and understanding during this journey.
Warm Regards, Patrik Simek
<details> <summary>The original Readme is available here.</summary>
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 the sandbox's console output
- The sandbox has limited access to the process's methods
- It is possible to require modules (built-in and external) from the sandbox
- You can limit access to certain (or all) built-in modules
- You can securely call methods and exchange data and callbacks between sandboxes
- Is immune to all known methods of attacks
- Transpiler support
How does it work
- It uses the internal VM module to create a secure context.
- It uses Proxies to prevent escaping from the sandbox.
- It overrides the built-in 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()');
// Throws ReferenceError: process is not defined
Installation
IMPORTANT: VM2 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,
root: './'
}
});
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
- Debugging a sandboxed code
- Read-only objects
- Protected objects
- Cross-sandbox relationships
- CLI
- 2.x to 3.x changes
- 1.x and 2.x docs
- Contributing
VM
VM is a simple sandbox to synchronously run untrusted code without the require
feature. Only JavaScript built-in objects and Node's Buffer
are available. Scheduling functions (setInterval
, setTimeout
and setImmediate
) are not available by default.
Options:
timeout
- Script timeout in milliseconds. WARNING: You might want to use this option together withallowAsync=false
. Further, operating on returned objects from the sandbox can run arbitrary code and circumvent the timeout. One should test if the returned object is a primitive withtypeof
and fully discard it (doing logging or creating error messages with such an object might also run arbitrary code again) in the other case.sandbox
- VM's global object.compiler
-javascript
(default) orcoffeescript
or custom compiler function. The library expects you to have coffee-script pre-installed if the compiler is set tocoffeescript
.eval
- If set tofalse
any calls toeval
or function constructors (Function
,GeneratorFunction
, etc.) will throw anEvalError
(default:true
).wasm
- If set tofalse
any attempt to compile a WebAssembly module will throw aWebAssembly.CompileError
(default:true
).allowAsync
- If set tofalse
any attempt to run code usingasync
will throw aVMError
(default:true
).
IMPORTANT: Timeout is only effective on synchronous code that you run through run
. Timeout does NOT work on any method returned by VM. There are some situations when timeout doesn't work - see #244.
const {VM} = require('vm2');
const vm = new VM({
timeout: 1000,
allowAsync: false,
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
allows you to require modules in the same way that you would in the 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) orcoffeescript
or custom compiler function (which receives the code, and it's file path). The library expects you to have coffee-script pre-installed if the compiler is set tocoffeescript
.eval
- If set tofalse
any calls toeval
or function constructors (Function
,GeneratorFunction
, etc.) will throw anEvalError
(default:true
).wasm
- If set tofalse
any attempt to compile a WebAssembly module will throw aWebAssembly.CompileError
(default:true
).sourceExtensions
- Array of file extensions to treat as source code (default:['js']
).require
-true
, an object or a Resolver to enablerequire
method (default:false
).require.external
- Values can betrue
, an array of allowed external modules, or an object (default:false
). All paths matching/node_modules/${any_allowed_external_module}/(?!/node_modules/)
are allowed to be required.require.external.modules
- Array of allowed external modules. Also supports wildcards, so specifying['@scope/*-ver-??]
, for instance, will allow using all modules having a name of the form@scope/something-ver-aa
,@scope/other-ver-11
, etc. The*
wildcard does not match path separators.require.external.transitive
- Boolean which indicates if transitive dependencies of external modules are allowed (default:false
). WARNING: When a module is required transitively, any module is then able to require it normally, even if this was not possible before it was loaded.require.builtin
- Array of allowed built-in modules, accepts ["*"] for all (default: none). WARNING: "*" can be dangerous as new built-ins can be added.require.root
- Restricted path(s) where local modules can be required (default: every path).require.mock
- Collection of mock modules (both external or built-in).require.context
-host
(default) to require modules in the host and proxy them into the sandbox.sandbox
to load, compile, and require modules in the sandbox.callback(moduleFilename, ext)
to dynamically choose a context per module. The default will be sandbox is nothing is specified. Except forevents
, built-in modules are always required in the host and proxied into the sandbox.require.import
- An array of modules to be loaded into NodeVM on start.require.resolve
- An additional lookup function in case a module wasn't found in one of the traditional node lookup paths.require.customRequire
- Use instead of therequire
function to load modules from the host.require.strict
-false
to not force strict mode on modules loaded by require (default:true
).require.fs
- Custom file system implementation.nesting
- WARNING: Allowing this is a security risk as scripts can create a NodeVM which can require any host module.true
to enable VMs nesting (default:false
).wrapper
-commonjs
(default) to wrap script into CommonJS wrapper,none
to retrieve value returned by the script.argv
- Array to be passed toprocess.argv
.env
- Object to be passed toprocess.env
.strict
-true
to loaded modules in strict mode (default:false
).
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: () => '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 the full path of the script you're running as a second argument to vm's run
method if the script is a string. The filename is then displayed in any stack traces generated by the script.
vm.run('require("foobar")', '/data/myvmscript.js');
If the script you are running is a VMScript, the path is given in the VMScript constructor.
const script = new VMScript('require("foobar")', {filename: '/data/myvmscript.js'});
vm.run(script);
Resolver
A resolver can be created via makeResolverFromLegacyOptions
and be used for multiple NodeVM
instances allowing to share compiled module code potentially speeding up load times. The first example of NodeVM
can be rewritten using makeResolverFromLegacyOptions
as follows.
const resolver = makeResolverFromLegacyOptions({
external: true,
builtin: ['fs', 'path'],
root: './',
mock: {
fs: {
readFileSync: () => 'Nice try!'
}
}
});
const vm = new NodeVM({
console: 'inherit',
sandbox: {},
require: resolver
});
VMScript
You can increase performance by using precompiled scripts. The precompiled VMScript can be run 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));
It 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 the first time it runs. One 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);
});
Debugging a sandboxed code
You can debug or inspect code running in the sandbox as if it was running in a normal process.
- You can use breakpoints (which requires you to specify a script file name)
- You can use
debugger
keyword. - You can use step-in to step inside the code running in the sandbox.
Example
/tmp/main.js:
const {VM, VMScript} = require('.');
const fs = require('fs');
const file = `${__dirname}/sandbox.js`;
// By providing a file name as second argument you enable breakpoints
const script = new VMScript(fs.readFileSync(file), file);
new VM().run(script);
/tmp/sandbox.js
const foo = 'ahoj';
// The debugger keyword works just fine everywhere.
// Even without specifying a file name to the VMScript object.
debugger;
Read-only objects (experimental)
To prevent sandboxed scripts from adding, changing, or deleting properties from the proxied objects, you can use freeze
methods to make the object read-only. This is only effective inside VM. Frozen objects are affected deeply. Primitive types cannot be frozen.
Example without using 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 freeze
:
const vm = new VM(); // Objects specified in the sandbox cannot be frozen.
vm.freeze(util, 'util'); // Second argument adds object to global.
vm.run('util.add = (a, b) => a - b'); // Fails silently when not in strict mode.
console.log(util.add(1, 1)); // returns 2
IMPORTANT: It is not possible to freeze objects that have already been proxied to the VM.
Protected objects (experimental)
Unlike freeze
, this method allows sandboxed scripts to add, change, or delete properties on objects, with one exception - it is not possible to attach functions. Sandboxed scripts are therefore not able to modify methods like toJSON
, toString
or inspect
.
IMPORTANT: It is not possible to protect objects that have already been proxied to the VM.
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 the command line, install it globally with npm install vm2 -g
.
vm2 ./script.js
Known Issues
- There are known security issues to circumvent the sandbox.
- It is not possible to define a class that extends a proxied class. This includes using a proxied class in
Object.create
. - Direct eval does not work.
- Logging sandbox arrays will repeat the array part in the properties.
- Source code transformations can result a different source string for a function.
- There are ways to crash the node process from inside the sandbox.
Deployment
- Update the
CHANGELOG.md
- Update the
package.json
version number - Commit the changes
- Run
npm publish