localeval-browseronly v1.0.0
Local Eval
Evaluate a string of JS code without access to the global object.
Always use that instead of eval(). Always.
API:
localeval(code :: String, sandbox :: Object) :: Object.
localeval(code :: String, sandbox :: Object,
timeout :: Number, cb :: Function)The code is a string of JS code. The sandbox contains objects which are
going to be accessible in the JS code.
It returns the last evaluated piece of JS code in code, if no timeout is
given. Otherwise, after at most timeout milliseconds, the callback gives that
result as a parameter: function(error, result) {…}.
Node example:
var localeval = require('localeval');
localeval('console.log("Do I have access to the console?")'); // Throws.
localeval.clear(); // Kills processes used internally.Browser example:
<!doctype html><title></title>
<script src='localeval.js'></script>
<!-- Alerts "32". -->
<script> alert(localeval('a + b', {a: 14, b: 18})) </script>You may find an example of use in browser code in main.html.
Purpose
Trying to find a reasonable cross-environment ES5 sandbox evaluation function.
Offering a process-separated timeout-ed VM for node.
Warning
If no timeout is given, it doesn't protect your single-threaded code against infinite loops. Additionally, the following leak:
({}).constructor.getOwnPropertyNames = function(){return 'leak';}Function("this.foo = 'leak'")()
If a timeout is given, an attacker can still use XHR:
Function("this.XMLHttpRequest(…); …")()
That said, it protects against any security leak.
All local and global variables are inaccessible.
Variables defined while evaluating code don't pollute any scope.
Evaluated code cannot fiddle with global object's properties. Think
localeval('([]).__proto__.push = function(a) { return "nope"; }').
Things to try
In comments are what should be executed outside the sandbox.
String.prototype.slice = function() { return 'leaked'; };
// 'nice'.slice(1) === 'ice'
String.fromCharCode = function() { return 'leaked'; };
// String.fromCharCode(42) === '*'
// var foo = 1
foo = 7
this.foo = 7
window.foo = 7
eval('foo = 7')
// foo === 1
delete Number.parseInt
// Number.parseInt('1337') === 1337
String.prototype.leak = function() { return 'leak'; }
// try { ''.leak() } catch(e) { /not a function/.test(e.message) }This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/.
8 years ago