Affected: patriksimek vm2

vm2 before 3.11.8 contains a sandbox escape vulnerability in NodeVM that allows attackers to access the host __proto__ getter/setter through console._stdout and console._stderr. Attackers can overwrite EventEmitter.prototype.emit and trigger process events to execute code with process context, bypassing code generation restrictions.

Affected: npm: vm2

## 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...

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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…