vm2 before 3.11.4 Defense Invariant Violation via setup-sandbox.js

Summary

vm2 is a sandbox for running untrusted JavaScript. In vm2 versions up to and including 3.11.3, the defaultSandboxPrepareStackTrace function in lib/setup-sandbox.js builds its output array using prototype-walking index assignment (lines[lines.length] = value) rather than a prototype-bypassing define-property primitive. Because this bridge-internal array is allocated in the sandbox realm, code inside the sandbox can install an accessor on Array.prototype for the relevant index; the accessor is then invoked whenever the sandbox reads error.stack (or otherwise triggers Error.prepareStackTrace), allowing sandbox code to observe and intercept each stack-trace line written by the bridge. The same pattern is used in the error-handling (catch) branch. The values written are formatted strings only, so the practical impact is limited to an information side channel and a violation of vm2's bridge-container defense invariant rather than a sandbox escape; the vendor rates the issue Low. The issue is fixed in vm2 3.11.4, which installs each entry as an own data property via Reflect.defineProperty.

Timeline

1. Sep 17, 2026, 1:46 PM UTCCVE published
2. Sep 17, 2026, 3:39 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Sep 17, 2026, 3:40 PM UTCRecord last updated

Affected versions

• patriksimek vm2

  fixed in 3.11.4

• vm2npm

  fixed in 3.11.4

References 2