GHSA-qhwx-74w5-xhxq

## Summary

On Node.js 24 and newer, `vm2` can expose the host `node:test` module to sandboxed `NodeVM` code when the embedder explicitly allows the `node:test` builtin. Sandbox code can reach that module through `require('node:node:test')` and call `run()` with attacker-controlled `execArgv`.

`node:test.run()` starts a separate Node process for process-isolated test execution and forwards the supplied `execArgv` values to that process. Supplying `--eval=<JavaScript>` therefore executes arbitrary JavaScript in an unrestricted host Node process, outside the `NodeVM` sandbox.

The PoC confirms that direct sandbox imports of `fs`, `child_process`, `module`, and `process` remain denied before the spawned process imports host `fs` and writes a harmless marker.

## Affected versions and environment

- Package: `vm2` - Affected versions: `>=3.9.6, <=3.11.5` - Latest reproduced version: `3.11.5` - Reproduced runtime: Node.js `v24.18.0` - Exact path is not present on Node.js 22 because `module.builtinModules` does not expose the scheme-only `node:test` entry there - Configuration prerequisite:

```js require: { builtin: ['node:test'], external: false } ```

The lower version boundary was tested directly: `vm2@3.9.5` blocks `require('node:node:test')`, while `vm2@3.9.6` permits the exploit path. Representative releases through `3.11.5` were also reproduced.

## Root cause

The issue is a combination of builtin admission, generic host passthrough, and prefix normalization:

1. On Node.js 24+, `module.builtinModules` includes the scheme-only key `node:test`. 2. `lib/builtin.js` builds `BUILTIN_MODULES` from that array. The family-based `DANGEROUS_BUILTINS` protection does not include `test`, so `node:test` remains eligible. 3. When the embedder explicitly allows `node:test`, `addDefaultBuiltin()` stores it through the generic loader:

```js builtins.set(key, special ? special : vm => vm.readonly(hostRequire(key))); ```

4. In `lib/setup-node-sandbox.js`, `requireImpl()` strips one `node:` prefix before builtin lookup:

```js if (localStringPrototypeStartsWith(filename, 'node:')) { id = localStringPrototypeSlice(filename, 5); nmod = loadBuiltinModule(id); } ```

5. Consequently, sandbox code requesting `node:node:test` is normalized to the stored key `node:test` and receives a readonly proxy to the host module. 6. The readonly proxy does not make `node:test.run()` safe. Calls are forwarded to the host implementation, which accepts attacker-controlled `execArgv` for a newly spawned Node process. 7. `--eval=<attacker JavaScript>` runs outside vm2 and has normal host builtin access.

The doubled prefix is the reachability mechanism, but the security boundary failure is broader: the generic host-passthrough loader treats the `test` builtin family as safe even though its `run()` API can launch unrestricted Node processes.

## Proof of concept

From the `poc` directory:

```bash npm ci --ignore-scripts --no-audit --no-fund node repro.js ```

Expected successful result on Node.js 24+ includes:

```json { "vm2Version": "3.11.5", "nodeVersion": "v24.18.0", "markerExists": true, "childIsDistinctProcess": true, "marker": { "hostCodeExecution": true } } ```

The PoC writes only `host-rce-marker.json` in its own directory and does not invoke a shell, contact a network service, or access third-party data.

## Impact

An attacker who is intentionally permitted to execute untrusted JavaScript in the affected `NodeVM` configuration can escape the sandbox and execute arbitrary JavaScript under the embedder's operating-system identity.

This provides the spawned process with the host user's filesystem, environment, network, and process-execution permissions. It can therefore result in complete confidentiality, integrity, and availability impact for the hosting service.

## Suggested remediation

Treat the normalized `test` builtin family as dangerous before wildcard expansion and explicit builtin registration.

For example, add `test` to `DANGEROUS_BUILTINS` so the existing prefix and family checks reject both `node:test` and `node:test/reporters`:

```js const DANGEROUS_BUILTINS = new Set([ // existing entries 'test' ]); ```

If test helpers must be exposed, provide a sandbox-local wrapper through `mock` or `override` that does not expose `run()`, process isolation, `execArgv`, or other host process controls.

Recommended regression cases:

- explicit `builtin: ['node:test']` - wildcard builtin configurations - `require('node:test')` - `require('node:node:test')` - `node:test/reporters` and prefixed variants - direct low-level builtin registration - attempts to pass `--eval`, `--require`, or `--import` through test-runner process options [vm2-node-test-ghsa-submission.zip](https://github.com/user-attachments/files/29930119/vm2-node-test-ghsa-submission.zip)