NodeVM network builtin exclusions bypass via internal _http_client and _http_server

## Summary `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: ```js 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`: ```js if (builtins.indexOf(`-${name}`) === -1) { addDefaultBuiltin(res, name, hostRequire); } ``` But excluding `http` and `net` does not exclude internal siblings such as: ```text _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: ```text vm2: 3.11.2 Node.js: v25.9.0 ``` Run from the vm2 repository root: ```bash node poc/internal-http-builtin-network-bypass.js ``` [internal-http-builtin-network-bypass.js](https://github.com/user-attachments/files/27571182/internal-http-builtin-network-bypass.js) The PoC first confirms the intended restrictions work then bypasses them: ```text require("_http_client").ClientRequest(...) ``` This performs an HTTP request to a host-local service and reads the response. It also confirms: ```text require("_http_server").Server(...).listen(0) ``` This opens a listening HTTP socket from inside the sandbox. <img width="951" height="623" alt="Screenshot 2026-05-10 at 1 07 39 PM" src="https://github.com/user-attachments/assets/21bfb1ff-dd15-423a-92c4-0337cd07816c" /> ## Impact 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. ## Suggested fix 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: ```text _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.

Source published

29 May 2026 18:08:06 UTC

Source modified

12 Jun 2026 19:45:09 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Publisher rating · HIGH