safeEval.js

/*
  The MIT License (MIT)
  Copyright (c) 2016 Gildas Lormeau (Capsule Code)

  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.
*/

const safeEval = (() => {
    const sourceCode = (() => {
        const whitelist = ["Array", "ArrayBuffer", "Boolean", "Date", "DataView", "Error", "Float32Array", "Float64Array", "Infinity", "Int8Array", "Int16Array", "Int32Array", "JSON", "Map", "Math", "NaN", "Number", "Object", "Promise", "RegExp", "Set", "String", "Symbol", "Uint8Array", "Uint8ClampedArray", "Uint16Array", "Uint32Array", "WeakMap", "WeakSet", "atob", "btoa", "decodeURI", "decodeURIComponent", "encodeURI", "encodeURIComponent", "escape", "isNaN", "parseFloat", "parseInt", "undefined", "unescape", "eval"];
        const scope = getScope(Object.create(null), window);
        delete Function.prototype.constructor;
        delete Object.getPrototypeOf(async () => { }).constructor;
        delete (function * () { }).prototype.constructor.constructor;
        return code => {
            with (scope) {
                return (function () {
                    "use strict";
                    return eval(`(0,eval)("eval = undefined"),${code}`);
                })();
            }
        };

        function getScope(scope, object) {
            Object.getOwnPropertyNames(object)
                .filter(name => whitelist.indexOf(name) == -1)
                .concat(["getScope", "scope", "whitelist"])
                .forEach(name => scope[name] = undefined);
            const proto = Object.getPrototypeOf(object);
            return proto ? getScope(scope, proto) : scope;
        }
    }).toString();

    return code => {
        const sandboxIframe = document.createElement("iframe");
        document.body.appendChild(sandboxIframe);
        const script = document.createElement("script");
        script.textContent = "var safeEval = (" + sourceCode + ")();";
        const sandboxWindow = sandboxIframe.contentWindow;
        sandboxWindow.document.body.appendChild(script);
        const safeEval = sandboxWindow.safeEval;
        document.body.removeChild(sandboxIframe);
        return safeEval(code);
    };
})();

let myFunction;
myFunction = safeEval("() => this");
console.log(myFunction()); // undefined

myFunction = safeEval("() => window");
console.log(myFunction()); // undefined

myFunction = safeEval("() => self");
console.log(myFunction()); // undefined

myFunction = safeEval("() => eval");
console.log(myFunction()); // undefined

myFunction = safeEval("() => (0,eval)");
console.log(myFunction()); // undefined

myFunction = safeEval("() => Object.getPrototypeOf(function() {}).constructor");
console.log(myFunction()); // undefined

myFunction = safeEval("() => Object.getPrototypeOf(async () => {}).constructor");
console.log(myFunction()); // undefined

myFunction = safeEval("() => Object.getPrototypeOf(function * () {}).constructor.constructor");
console.log(myFunction()); // undefined

@gildas-lormeau j'avoue la c'est tendu. J'ai vu que tu avais interdis eval aussi ^

safeEval(`
(async () => {
  const fn =  async () => {}
  const getter = new fn.constructor('return this')
  const global = await getter()
  return global.localStorage.clear()
})()
`)

Sous Canary version 56.0.2902.0 (64-bit), j'obtiens en retour de l'appel :

Promise
  __proto__: Promise
  [[PromiseStatus]]: "rejected"
  [[PromiseValue]]: TypeError: Cannot read property 'clear' of null at eval (eval at <anonymous> (:10:28), <anonymous>:6:29)

Faire du code sur mobile c'est pas une bonne idée ^^

Voila un meilleur exemple, j'arrive a retourner une promesse qui expose un objet censé etre blackboxé

safeEval(`
(async () => {
  const a =  async () => {}
  const b = new a.constructor('return this')
  const c = await b()
  const d = c.Function('return this')
  return d().setTimeout
})()
`).then(console.log)

La même avec les generateurs

safeEval(`
(() => {
  const g = function * () {}
  const code = "return setTimeout"
  const h = new g.prototype.constructor.constructor(code)()
  const setTimeout = h.next().value
  return setTimeout
})()
`)

Le fait que l'iframe soit créée et détruite de manière synchrone fait que l'effet de bord ne se voit pas, mais le contexte d'exécution de la fonction safeEval peut être bypassé par async/wait et les generateurs

J'ai mis à jour le gist (cf. https://gist.github.com/gildas-lormeau/3de0d4bbfce1873b0286ef7ce293f2ce#file-safeeval-js-L17-L18). Pour le coup, la défense est toujours la même, faut juste détruire tous ces constructeurs malicieux.

Pour info, j'ai vérifié dans la spec, constructor a la propriété configurable = true, donc on peut la détruire, y'a pas de hack.

Encore merci pour l'aide, je suis conscient de la prise de tête que ça représente ;-)

Ca a l'air super. Je vais jetter un coup d'oeil plus profond tres bientot.

Le problème, c'est qu'on ne peut pas définir des variables:

safeEval(x=1+2) cause un erreur:

Uncaught ReferenceError: x is not defined
    at eval (eval at <anonymous> (:11:28), <anonymous>:1:31)
    at <anonymous>:11:28
    at code (<anonymous>:12:19)
    at code (<anonymous>:36:16)
    at <anonymous>:1:1