CVE-2026-92948: vm2: NodeVM builtin allowlist bypass via node:test.run() execArgv allows sandbox escape

## 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: `[email protected]` blocks `require('node:node:test')`, while `[email protected]` 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)