CVE-2026-47209 Details

A vulnerability in vm2, an open-source sandbox for Node.js, exists in versions prior to 3.11.4. The issue arises because the BaseHandler.set trap in bridge.js ignores the receiver parameter and always writes to the host target object. This behavior violates the Proxy set trap specification, which requires property assignments to be made on the receiver when it differs from the proxy. As a result, inherited property writes can leak through to the host object. This vulnerability also provides an alternative method to write cross-realm Symbol keys, such as nodejs.util.promisify.custom, to host objects, bypassing any future safeguards. The vulnerability can be exploited by creating a child object that inherits from a host object and using the child to write properties, which will then appear on the host object.

Users can upgrade to vm2 version 3.11.4 or later, where this vulnerability has been patched.