vm2 sandbox escape on Node.js 26 through a stale PromiseThenLookupChain protector

## Reporter - Name or handle: `[YMsora]` - Report date: 2026-08-14 ## Summary The latest published vm2 release, **3.11.5**, and the current `main` branch are vulnerable to a sandbox escape when used on Node.js 26. An ordinary fulfilled Promise created by an async function can retain an attacker-controlled `constructor[Symbol.species]` across `Promise.prototype.finally()`. vm2 installs wrappers on the intrinsic `Promise.prototype.then` and `catch` methods. On Node.js 26 / V8 14.6, V8's `SetPrototypeProperties` path updates these existing data properties without invalidating the `PromiseThenLookupChain` protector. `Promise.prototype.finally()` subsequently trusts the stale protector and uses an internal `InvokeThen` fast path that calls the original native `then`, bypassing vm2's wrapper and its `resetPromiseSpecies(this)` hardening. The attacker-controlled species constructor therefore supplies the resolve and reject functions used by a native Promise reaction. A calibrated stack overflow at that native reaction boundary yields a raw host-realm `RangeError` to the attacker-controlled reject function. Its constructor chain reaches the host `Function` constructor and consequently the host `process` object. The attached proof is non-destructive: it reads only `process.version`. It does not execute commands, access files, or perform network requests. ## Latest-version status Verified on 2026-08-14: - npm `latest`: `vm2@3.11.5` - `vm2@3.11.5` publication time: 2026-05-18T15:37:26.1