NodeVM builtin denylist bypass via process and inspector/promises allows host code execution

## Summary `NodeVM` blocks several dangerous Node.js builtins such as `module`, `worker_threads`, `cluster`, `vm`, `repl`, and `inspector`. However, the denylist misses `process` and `inspector/promises`. Both can be used from sandboxed code to reach host-side execution primitives. This allows sandboxed code to bypass the intended builtin restrictions and execute code in the host process. ## Details The dangerous builtin denylist is defined in `lib/builtin.js`. This list does not include: ```text process inspector/promises ``` Non-denied builtins are exposed to the sandbox through: ```js builtins.set(key, special ? special : vm => vm.readonly(hostRequire(key))); ``` Because of this, sandboxed code can bypass the expected restrictions in two ways: 1. `require('process').getBuiltinModule('child_process')` reloads `child_process`, even when `child_process` is excluded. 2. `require('inspector/promises')` exposes the Inspector protocol and can call `Runtime.evaluate` in the host process. ## PoC Tested on: ```text vm2: 3.11.2 Node.js: v25.9.0 ``` Run from the vm2 repository root: ```bash node poc/dangerous-builtin-denylist-rce.js ``` [dangerous-builtin-denylist-rce.js](https://github.com/user-attachments/files/27570113/dangerous-builtin-denylist-rce.js) The PoC first confirms the intended restrictions work: ```text require("inspector"): BLOCKED require("child_process"): BLOCKED ``` Then it bypasses them: ```text require("process").getBuiltinModule("child_process").execFileSync(...) ``` This spawns a host child process. It also confirms: ```text require("inspector/promises").Session().post("Runtime.evaluate", ...) ``` This evaluates JavaScript in the host process. <img width="858" height="766" alt="Screenshot 2026-05-10 at 11 53 33 AM" src="https://github.com/user-attachments/assets/7614aecb-5ffd-4c41-bfe8-e1fcb3b1bb59" /> ## Impact An attacker who can run untrusted JavaScript inside `NodeVM` with affected builtin settings can escape the sandbox and execute arbitrary code in the host process. This can lead to full compromise of the application process, including reading files, writing files, spawning processes, and accessing host environment secrets. (This is not reachable with the default NodeVM configuration where require is disabled or no affected builtins are allowed. It affects applications that allow process, inspector/promises, or the wildcard "*" in require.builtin.) ## Suggested fix Add `process` and `inspector/promises` to the dangerous builtin blocklist. Also consider blocking dangerous builtin families by prefix, for example blocking both: ```text inspector inspector/* ``` instead of only exact module names.

Source published

29 May 2026 17:59:23 UTC

Source modified

12 Jun 2026 21:15:15 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:H/A:H

Publisher rating · CRITICAL