CVE-2026-92953: vm2: Default VM can mutate host TypedArray and ArrayBuffer intrinsics after the host-prototype pollution fix

vm2 guards host intrinsics through a protectedHostObjects set in lib/bridge.js. That set is built from a fixed list: Number, String, Boolean, Date, RegExp, Map, WeakMap, Set, WeakSet, Promise and Function. Typed arrays and ArrayBuffer are not on it.

Sandbox code can reach those host prototypes by walking __proto__ from a host Buffer, using __lookupGetter__. Because they are unprotected, bridge defineProperty writes land on the real host objects. The researcher's proof of concept installs marker properties and a method on all three prototypes. Ordinary host typed arrays and ArrayBuffers then show them after VM.run() has finished.

The attacker needs only the ability to run JavaScript in a default VM. No NodeVM, require, wildcard builtins or nesting is needed. The report claims integrity and availability impact, not direct command execution or data disclosure. A host that later trusts typed-array behavior, for example in parsing, crypto or serialization, can be made to misbehave or crash. The release notes add that iterator prototypes were also unprotected.

vm2 versions from 3.11.0 up to and including 3.11.7 with the default VM. The reporter also reproduced it on 3.10.0 to 3.10.5, which the earlier advisory already covers. Check what you run:

npm ls vm2

Check transitive dependencies too.

Upgrade to vm2 3.11.8.

npm install [email protected]

The fix extends the protected-intrinsics list to ArrayBuffer, SharedArrayBuffer, DataView, every TypedArray and the iterator prototypes. The release notes call it transparent to correct sandbox code and list no workaround. After the patch, the same writes throw VMError: Operation not allowed on contextified object.

No log line records the attack. Search stored or submitted sandbox code for __lookupGetter__ combined with Buffer.apply, or for repeated __proto__ getter calls on a Buffer. In a running host process, compare Object.getOwnPropertyNames(Uint8Array.prototype) and ArrayBuffer.prototype against a clean process. Unexpected extra properties point to pollution. Restart the process to clear it, then upgrade.

Summary

vm2's current host-intrinsic prototype protection is incomplete. The fix for GHSA-vwrp-x96c-mhwq blocks sandbox writes into classic host intrinsics such as Object.prototype, Array.prototype, and Function.prototype, but current head still lets sandbox code in a default VM reach and mutate host Uint8Array.prototype, %TypedArray%.prototype, and ArrayBuffer.prototype.

After VM.run() returns, normal host typed-array and ArrayBuffer objects observe attacker-controlled properties and methods installed by the sandbox.

Technical Details

The existing mitigation relies on protectedHostObjects in lib/bridge.js. That set is populated from otherGlobalPrototypes, which is built from a fixed inventory of classic globals:

const globalsList = [
  'Number', 'String', 'Boolean', 'Date', 'RegExp', 'Map', 'WeakMap',
  'Set', 'WeakSet', 'Promise', 'Function'
];

The inventory omits typed-array and ArrayBuffer intrinsics. Sandbox code can still reuse the host-prototype walking primitive from the prior public advisory:

const lookupGetter = ({}).__lookupGetter__;
const apply = Buffer.apply;
const protoGetter = apply.apply(lookupGetter, [Buffer, ['__proto__']]);
const hostBuffer = Buffer.from([1]);

const hostBufferPrototype = protoGetter.call(hostBuffer);
const hostUint8ArrayPrototype = protoGetter.call(hostBufferPrototype);
const hostTypedArrayPrototype = protoGetter.call(hostUint8ArrayPrototype);
const hostArrayBufferPrototype = protoGetter.call(hostBuffer.buffer);

Those objects are not sandbox-local. Inside the sandbox, hostUint8ArrayPrototype === Uint8Array.prototype, hostTypedArrayPrototype === Object.getPrototypeOf(Uint8Array.prototype), and hostArrayBufferPrototype === ArrayBuffer.prototype are all false. Because the objects are not in protectedHostObjects, bridge defineProperty writes are forwarded into the real host objects.

This is the same guard-coverage boundary as the previous host-intrinsic prototype pollution fix, but with a missing intrinsic family. The bridge already has the correct enforcement shape; the protected inventory is too narrow.

PoC

PoV: poc/pov-host-typedarray-arraybuffer-prototype-pollution.js

Current-head output:

{
  "status": "completed",
  "vulnerable": true,
  "node": "v25.8.0",
  "v8": "14.1.146.11-node.20",
  "control": {
    "defineResult": true,
    "sandboxReadsBack": "sandbox-only",
    "hostControlAfter": null
  },
  "exploit": {
    "hostUint8IsSandboxUint8": false,
    "hostTypedArrayIsSandboxTypedArray": false,
    "hostArrayBufferIsSandboxArrayBuffer": false,
    "defineUint8": true,
    "defineTypedArray": true,
    "defineArrayBuffer": true,
    "defineMethod": true
  },
  "hostEffect": {
    "uint8Marker": "polluted-host-uint8array-prototype",
    "typedArrayMarker": "polluted-host-typedarray-prototype",
    "arrayBufferMarker": "polluted-host-arraybuffer-prototype",
    "methodReturn": "sandbox-method-reached-host-uint8array"
  }
}

The control proves sandbox-local Uint8Array.prototype writes remain sandbox-local. The exploit path reaches host prototypes through the bridge and causes host-created objects to observe sandbox-installed properties after VM.run() returns.

Impact

This is a sandbox boundary violation and host intrinsic prototype pollution. An attacker who can run JavaScript in a default vm2 VM can mutate shared host typed-array and ArrayBuffer behavior without NodeVM, require, wildcard builtins, nesting: true, or any host-provided typed-array object.

The supplied PoV demonstrates integrity and availability impact by installing markers and a method on host prototypes:

• Uint8Array.prototype
• %TypedArray%.prototype, which affects typed-array families through the shared typed-array prototype chain
• ArrayBuffer.prototype

The PoV does not claim direct host command execution or direct confidentiality impact. It is local-only and restores touched descriptors before exit.

Suggested Fix

Extend the protected host-object inventory and identity/prototype mappings to typed-array and binary-data intrinsics, including at least:

• %TypedArray%.prototype
• ArrayBuffer.prototype
• SharedArrayBuffer.prototype when present
• DataView.prototype
• all concrete typed-array prototypes present in the runtime, including Uint8Array.prototype, Uint8ClampedArray.prototype, Int8Array.prototype, Uint16Array.prototype, Int16Array.prototype, Uint32Array.prototype, Int32Array.prototype, Float16Array.prototype when present, Float32Array.prototype, Float64Array.prototype, BigInt64Array.prototype, and BigUint64Array.prototype

A temporary patched-control that added this intrinsic family to thisGlobalPrototypes caused the same PoV's Reflect.defineProperty() calls to throw VMError: Operation not allowed on contextified object, and no host markers were installed.

The fix should cover the same host mutation traps used by the existing host-intrinsic protection: set, defineProperty, deleteProperty, and preventExtensions. It should not special-case Buffer; Buffer is only one way to reach the omitted host prototypes.

Affected Package/Versions

Confirmed on current head 7a1f5100b96f48d34e0fe104ab37c0acc5944f92 / v3.11.5 with Node v25.8.0 / V8 14.1.146.11-node.20.

Confirmed affected after the prior patch: npm:vm2 >= 3.11.0, <= 3.11.5.

Local sweep also reproduces on v3.10.0 through v3.10.5, but that range overlaps the already-published GHSA-vwrp-x96c-mhwq range. v3.9.0 through v3.9.2 did not produce host-visible pollution in the same local test.

Why This Is Not Intended Behavior

vm2 documents VM as a sandbox for untrusted code without require, with only JavaScript built-ins and Node's Buffer available by default. The known escape hatches do not explain this issue:

• require.builtin: ['*'] is a NodeVM configuration; this PoV uses default VM.
• nesting: true is not enabled or used.
• The README timeout caveat covers host code operating on objects returned from the sandbox; this PoV mutates host intrinsics and later affects ordinary host-created typed arrays and ArrayBuffers.

The project's own attack notes state that host-realm intrinsic prototypes should be protected from sandbox writes, while non-intrinsic host objects may remain mutable when intentionally exposed. Typed-array and ArrayBuffer prototypes are host intrinsics, not embedder-owned application objects.

Buffer availability explains how the PoV reaches the host prototype chain, but it does not authorize mutation of unrelated host-realm intrinsics. The host effects are observed on new host-created typed arrays and ArrayBuffers after VM.run() returns; the host is not invoking an object returned from the sandbox.