NodeVM observability builtins leak host process and HTTP request data

Summary

NodeVM exposes some process-wide observability builtins when they are allowed through require.builtin.

The following builtins are not blocked by the dangerous builtin denylist:

diagnostics_channel
async_hooks
perf_hooks

These modules are process-wide, not sandbox-local. Sandboxed code can use them to observe host application data across the vm2 boundary.

Note: It is a host data exposure issue. The impact depends on whether the host application allows these builtins and uses HTTP, async request context, diagnostics channels, or performance marks in the same process.

Details

Non-denied builtins are exposed to the sandbox through lib/builtin.js:

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

diagnostics_channel, async_hooks, and perf_hooks are not denied. These modules expose host process state rather than sandbox-local state.

Confirmed examples:

1. diagnostics_channel lets sandboxed code subscribe to Node.js HTTP diagnostic channels such as http.server.request.start. The sandbox receives host HTTP request objects and can read headers such as Authorization or session tokens.
2. async_hooks.executionAsyncResource() lets sandboxed code read the current host AsyncResource. If the host stores request/user data on that resource, the sandbox can read it.
3. perf_hooks.performance.getEntriesByType('mark') lets sandboxed code read host performance timeline entries.

PoC

Run from the vm2 repository root:

node poc/observability-builtins-info-leak.js

observability-builtins-info-leak.js

The PoC uses only the specific builtin being tested in each section.

It confirms:

diagnostics_channel: sandbox reads host HTTP request headers
async_hooks: sandbox reads host AsyncResource data
perf_hooks: sandbox reads host performance mark names

Example impact from the PoC:

authorization: Bearer HOST_HTTP_SECRET_...
x-session-token: HOST_HTTP_SECRET_...

These values are sent to a host HTTP server, but the sandbox reads them through diagnostics_channel.

<img width="997" height="566" alt="Screenshot 2026-05-10 at 1 13 20 PM" src="https://github.com/user-attachments/assets/36a7d600-8b53-4bfe-ab06-4e6dcfad5015" />

Impact

An attacker who can run untrusted JavaScript inside NodeVM with affected builtin settings can observe data from the host process.

In a real application, this may expose HTTP request headers, authorization tokens, session tokens, request context values, user identifiers, or other sensitive diagnostics data from the host application or from other users.

Suggested fix

Treat process-wide observability modules as dangerous builtins for untrusted sandboxes.

At minimum, consider blocking:

diagnostics_channel
async_hooks
perf_hooks

These modules are not sandbox-local and can expose host process state across the vm2 boundary.