vm2: util.getCallSites() bypasses GHSA-v27g-jcqj-v8rw host-frame redaction, leaks host call stack

Summary

NodeVM exposes the host util module to the sandbox through an unfiltered shallow copy (Object.assign({}, util)). On Node.js >= 22.9 this hands sandboxed code util.getCallSites(), a programmatic stack-introspection API that returns the host process's full call stack — absolute file paths, function names, and line numbers — including vm2 bridge internals and the embedding application's entrypoint. This bypasses the host-frame redaction established in GHSA-v27g-jcqj-v8rw, which only covers the Error.prepareStackTrace channel.

Details

• Root cause — defaultBuiltinLoaderUtil copies every static member of the host util module and wraps the copy in vm.readonly() without filtering any member, so newly added Node APIs land in the sandbox automatically: https://github.com/patriksimek/vm2/blob/7a1f5100b96f48d34e0fe104ab37c0acc5944f92/lib/builtin.js#L25-L38
• Second equivalent channel — the deprecated sys builtin (an alias of host util) goes through the generic builtin loader vm.readonly(hostRequire(key)), which also carries getCallSites: https://github.com/patriksimek/vm2/blob/7a1f5100b96f48d34e0fe104ab37c0acc5944f92/lib/builtin.js#L230
• Bypassed protection — GHSA-v27g's redaction (isHostFrameFileName + applyCallSiteGetters) rewrites host-frame metadata getters to null only when the *sandbox realm* formats an error stack: https://github.com/patriksimek/vm2/blob/7a1f5100b96f48d34e0fe104ab37c0acc5944f92/lib/setup-sandbox.js#L818-L870

util.getCallSites() produces its data host-side and never passes through that formatter, so frames such as lib/bridge.js @apply (the bridge apply trap), lib/nodevm.js @run, the embedder's own entry file, and node:internal/* frames reach the sandbox verbatim as data properties (scriptName, functionName, lineNumber, columnNumber, scriptId). A repository-wide grep (source, docs/ATTACKS.md, CHANGELOG, tests) shows no occurrence of getCallSites; the member was never considered.

PoC

Prerequisites: Node.js >= 22.9 (verified on v22.23.1); run npm ci --no-audit --no-fund at the repository root.

One-line reproducer (prints /workspace/repo/lib/bridge.js, i.e. a vm2-internal host path):

node -e "const {NodeVM}=require('/workspace/repo'); console.log(new NodeVM({require:{builtin:['util']}}).run(\"module.exports = require('util').getCallSites(4)[0].scriptName\"))"

Observed frames inside the sandbox, with both require: { builtin: ['util'] } and require: { builtin: ['*'] }:

/workspace/repo/lib/bridge.js @apply:1664 vm.js @:5 /workspace/repo/lib/bridge.js @apply:1664 /workspace/repo/lib/nodevm.js @run:563 /workspace/out/<embedder entrypoint>.js @main:29 node:internal/modules/cjs/loader @:1781 node:internal/modules/cjs/loader @:1913 ... (8 node:internal/* frames in total)

Impact

Information disclosure. Any NodeVM configuration that allows the util (or sys) builtin — including the wildcard builtin: ['*'], both typical configurations from the README — lets untrusted sandboxed code programmatically read the host call stack: the vm2 installation path, the embedding application's file layout and entrypoint, and internal function names and line numbers. This is the same information category redacted by GHSA-v27g-jcqj-v8rw (Defense Invariant #5 in docs/ATTACKS.md) and breaks defense-in-depth assumptions of embedders that rely on host frames being invisible to the sandbox. The API returns only strings/numbers (no host object references); no escalation to code execution was identified.

Suggested fix: filter members in defaultBuiltinLoaderUtil (allowlist, or at minimum drop getCallSites), apply the same treatment to the generic loader path used by sys, and extend the GHSA-v27g regression tests to cover programmatic stack-introspection APIs.