GHSA-mpf8-4hx2-7cjg MEDIUM npm/vm2

CVE: CVE-2026-44000

Summary

A sandbox boundary violation in vm2 allows host object identity to cross into the sandbox through host Promise resolution.

When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox .then() callback preserves host identity. This allows the sandbox to interact with the host object directly, including:

• Performing identity checks using host-side WeakMap
• Mutating host object state from inside the sandbox

This behavior occurs because the Promise fulfillment wrapper uses ensureThis() instead of the stronger cross-realm conversion path (from() / proxy wrapping). If no prototype mapping is found, ensureThis() returns the original object.

As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation.

Details

In setup-sandbox.js, vm2 wraps Promise.prototype.then:

globalPromise.prototype.then = function then(onFulfilled,onRejected) {resetPromiseSpecies(this);if (typeof onFulfilled === 'function') {const origOnFulfilled = onFulfilled;onFulfilled = function onFulfilled(value) {value = ensureThis(value);return apply(origOnFulfilled,this,[value]);};}return apply(globalPromiseThen,this,[onFulfilled,onRejected]);};
The wrapper calls ensureThis(value) before invoking the sandbox callback.

However,ensureThis is implemented in bridge.js as thisEnsureThis():

function thisEnsureThis(other) {const type = typeof other;switch (type) {case 'object':
      if (other === null) return null;case 'function':
      let proto = thisReflectGetPrototypeOf(other);if (!proto) {return other;}while (proto) {
const mapping = thisReflectApply(thisMapGet,protoMappings,[proto]);if (mapping) {const mapped = thisReflectApply(thisWeakMapGet,mappingOtherToThis,[other]);if (mapped) return mapped;return

📌 来源: GitHub-Advisory | 🆔 CVE-2026-44000 | 📅 2026-05-07