CVE-2026-47139

NodeVM supports excluding public network builtins from the wildcard builtin option. With this configuration direct access to http, https, http2, net, dgram, tls, dns, and dns/promises is blocked.

However, Node.js also exposes underscored internal HTTP builtins such as _http_client and _http_server. These are not blocked when the public modules are excluded.

Sandboxed code can use these internal builtins to make outbound HTTP requests and open listening HTTP sockets even though the public network modules are denied.

Note: This is not host RCE. It is a network capability bypass that can lead to SSRF-style access to internal services.

Details

The wildcard builtin expansion is based on Node.js builtin module names:

const BUILTIN_MODULES = (nmod.builtinModules || Object.getOwnPropertyNames(process.binding('natives')))
  .filter(s=>!s.startsWith('internal/') && !DANGEROUS_BUILTINS.has(s));

Public modules can be excluded with -name:

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

But excluding http and net does not exclude internal siblings such as:

_http_client
_http_server
_tls_wrap

These internal modules expose network primitives.

Confirmed examples:

1. require('_http_client').ClientRequest(...) performs an outbound HTTP request to a host-local service while http and net are blocked.
2. require('_http_server').Server(...).listen(...) opens a listening HTTP socket while http and net are blocked.

PoC

Tested on:

vm2: 3.11.2
Node.js: v25.9.0

Run from the vm2 repository root:

node poc/internal-http-builtin-network-bypass.js

internal-http-builtin-network-bypass.js

The PoC first confirms the intended restrictions work then bypasses them:

require("_http_client").ClientRequest(...)

This performs an HTTP request to a host-local service and reads the response.

It also confirms:

require("_http_server").Server(...).listen(0)

This opens a listening HTTP socket from inside the sandbox.

An attacker who can run untrusted JavaScript inside NodeVM with this affected builtin configuration can regain network access even when the application attempted to block network modules.

This can allow SSRF-style access to localhost services, metadata endpoints, internal admin panels, or other network resources reachable from the host process.

CVE-2026-47139 has a CVSS score of 8.6 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.11.4); upgrading removes the vulnerable code path.

Kodem intelligence

Treat underscored internal network modules as dangerous or link their availability to the public module they wrap.

At minimum, exclude related internal modules such as:

_http_agent
_http_client
_http_common
_http_incoming
_http_outgoing
_http_server
_tls_common
_tls_wrap

Alternatively, deny underscored Node.js internals from wildcard builtin expansion by default.

1. What is CVE-2026-47139? CVE-2026-47139 is a high-severity security vulnerability in vm2 (npm), affecting versions <= 3.11.3. It is fixed in 3.11.4.
2. How severe is CVE-2026-47139? CVE-2026-47139 has a CVSS score of 8.6 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of vm2 are affected by CVE-2026-47139? vm2 (npm) versions <= 3.11.3 is affected.
4. Is there a fix for CVE-2026-47139? Yes. CVE-2026-47139 is fixed in 3.11.4. Upgrade to this version or later.
5. Is CVE-2026-47139 exploitable, and should I be worried? Whether CVE-2026-47139 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47139 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47139? Upgrade vm2 to 3.11.4 or later.