| Package | Affected versions | Patched versions |
|---|---|---|
| vm2 | ≥ 3.10.2, < 3.11.7 | 3.11.7 |
[YMsora]The latest published vm2 release, 3.11.5, and the current main branch are vulnerable to a sandbox escape when used on Node.js 26. An ordinary fulfilled Promise created by an async function can retain an attacker-controlled constructor[Symbol.species] across Promise.prototype.finally().
vm2 installs wrappers on the intrinsic Promise.prototype.then and catch methods. On Node.js 26 / V8 14.6, V8's SetPrototypeProperties path updates these existing data properties without invalidating the PromiseThenLookupChain protector. Promise.prototype.finally() subsequently trusts the stale protector and uses an internal InvokeThen fast path that calls the original native then, bypassing vm2's wrapper and its resetPromiseSpecies(this) hardening.
The attacker-controlled species constructor therefore supplies the resolve and reject functions used by a native Promise reaction. A calibrated stack overflow at that native reaction boundary yields a raw host-realm RangeError to the attacker-controlled reject function. Its constructor chain reaches the host Function constructor and consequently the host process object.
The attached proof is non-destructive: it reads only process.version. It does not execute commands, access files, or perform network requests.
Verified on 2026-08-14:
latest: [email protected][email protected] publication time: 2026-05-18T15:37:26.138ZgitHead: 7a1f5100b96f48d34e0fe104ab37c0acc5944f92https://registry.npmjs.org/vm2/-/vm2-3.11.5.tgzsha512-RSrkBiwrj6FRU+QdqNs6KG0XdlvJCjpQ4GXiqmMbrhmwfu5k/XIMpAer0L8f6iuf0uJ3a4T1xJN126Q8yf0VIA==main HEAD: the same commit, also tagged v3.11.5v26.7.0, V8 14.6.202.34The npm tarball and current GitHub main contain the same relevant lib/setup-sandbox.js Git blob. There is no unpublished fix on main at the time of this report.
Permanent source reference:
| vm2 version | Result |
|---|---|
| 3.10.2 through 3.10.5 | host realm reached, 3/3 per release |
| 3.11.0 | host realm reached, 3/3 |
| 3.11.1 | host realm reached, 3/3 |
| 3.11.2 | host realm reached, 5/5 |
| 3.11.3 | host realm reached, 3/3 |
| 3.11.4 | host realm reached, 5/5 |
| 3.11.5 | host realm reached, 5/5 |
current main (7a1f5100) | host realm reached, 5/5 |
This report therefore confirms vm2 3.10.2 through 3.11.5 as affected when used with the vulnerable runtime. Earlier vm2 versions are not claimed: they may be independently vulnerable through older published issues, which would not establish this root cause.
| Node.js | V8 | Result |
|---|---|---|
| 22.23.2 | 12.4.254.21 | safe, 5/5 |
| 24.19.0 | 13.6.233.17 | safe, 5/5 |
| 25.9.0 | 14.1.146.11 | safe, 5/5 |
| 26.0.0 | 14.6.202.33 | host realm reached, 5/5 |
| every formal release from 26.1.0 through 26.7.0 | 14.6.202.34 | host realm reached, 5/5 per release |
| v27.0.0-nightly202608131b2de5e052 | 14.6.202.34 | host realm reached |
| v27.0.0-v8-canary20260812f3fe529a1e | 15.3.55 | safe |
The vulnerable behavior was reproduced on Linux/musl, Linux/glibc, and Windows x64. It is not Alpine-specific.
The default configuration is affected:
const vm = new VM();
Default new VM() was verified 3/3 on Node.js 26.7.0 and vm2 3.11.5 with the operating system's default Node stack size.
The escape also remains reproducible with stronger settings:
const vm = new VM({
allowAsync: true,
eval: false,
wasm: false,
timeout: 5000
});
Therefore the exploit does not require:
The demonstrated producer uses an async function, so async support must be available. This is vm2's default.
The V8 PromiseThenLookupChain protector must still be intact when vm2 installs its wrappers. A fresh/default Node.js process satisfies this condition. An unrelated earlier mutation that correctly invalidates the protector can make this exact path safe, but that is not a documented vm2 mitigation and is not present in the default setup.
The attachment poc.js uses only the published npm package and prints a benign host-version marker.
mkdir vm2-node26-repro
cd vm2-node26-repro
npm init -y
npm install --ignore-scripts --no-audit --no-fund [email protected]
cp /path/to/poc.js .
node poc.js
Alternatively, with the official Node.js 26.7.0 container:
docker run --rm -v "$PWD:/poc:ro" -w /tmp node:26.7.0-bookworm-slim sh -lc '
npm init -y >/dev/null 2>&1 &&
npm install --ignore-scripts --no-audit --no-fund [email protected] >/dev/null 2>&1 &&
cp /poc/poc.js . &&
node poc.js
'
Representative output:
{
"node": "v26.7.0",
"v8": "14.6.202.34-node.28",
"vm2": "3.11.5",
"config": "default",
"result": "HOST",
"hostVersion": "v26.7.0",
"speciesCalls": 1,
"localError": false,
"localRangeError": false
}
The calibrated depth varies with the platform and process layout; this is expected. The PoC searches the boundary instead of relying on a fixed depth.
To verify that disabling eval and WebAssembly is not sufficient:
STRICT=1 node poc.js
Promise.prototype.then and catch methods with wrappers that sanitize callbacks and execute resetPromiseSpecies(this).lib/setup-sandbox.js.proto_assign_seq_opt optimization, combining this assignment sequence into SetPrototypeProperties.Object::SetDataProperty(&it, value) without first calling it.UpdateProtector().PromiseThenLookupChain protector incorrectly remains valid.Promise.prototype.finally() performs an internal InvokeThen. Because the protector appears valid, V8 directly selects the native Promise then instead of performing the observable property lookup that would reach vm2's wrapper.constructor[Symbol.species] is not reset before the native then creates its result capability.RangeError and passes it to the attacker-provided capability reject function without vm2 conversion.error.constructor.constructor is consequently the host Function, even when the VM was configured with eval:false.The root-cause control is strong:
node --no-proto-assign-seq-opt poc.js
On Node.js 26.7.0 this changes the result from HOST to SAFE (3/3). A separate semantic probe also changes from wrapperCalls=0 to wrapperCalls=1.
This report intentionally discloses the overlap with prior work:
That issue concerned bypassing callback sanitization on intrinsic Promises returned by async functions. vm2's fix added/strengthened the globalPromise.prototype.then and catch wrappers. The current issue is different: on V8 14.6, finally() trusts a stale protector and bypasses those installed wrappers at the engine fast path.
That issue used a missing resetPromiseSpecies call in localPromise's rejection-swallowing tail. It is marked fixed in 3.11.4. The current entry point is the intrinsic async Promise plus finally()/InvokeThen; the PoC succeeds against 3.11.4 and 3.11.5.
That issue required a JSPI-backed Promise and WebAssembly APIs. Its 3.11.4 fix removes the relevant JSPI surface. The current PoC uses an ordinary fulfilled async-function Promise, works with wasm:false, and succeeds against 3.11.5.
The underlying V8 protector bookkeeping bug is already public and fixed upstream:
This report does not claim discovery of a new V8 bug. It reports a previously undocumented, still-unpatched vm2 sandbox escape created by the interaction between that V8 bug and vm2's Promise hardening. The escape affects vm2's latest release and current main branch.
An attacker who can execute untrusted JavaScript inside a vm2 VM can cross the sandbox boundary and obtain the host Function constructor and process object. This permits arbitrary code execution with the privileges of the host Node.js process, including access to its filesystem, credentials, environment, network, and child-process facilities.
This is the exact security boundary vm2 is intended to enforce; no additional application mistake is required beyond executing attacker-controlled code in the sandbox.
then and catch wrappers through an operation that reliably invalidates V8's Promise lookup-chain protector, such as an appropriate Reflect.defineProperty/Object.defineProperty path, instead of the optimizable consecutive direct-assignment sequence.Promise.prototype.finally entry point and execute resetPromiseSpecies(this) before delegating to the cached native finally implementation.(async () => 1)(): an attacker-controlled own species must not be constructed by p.finally().Verified controls show that wrapping finally before calling the cached native implementation blocks the tested direct variants, while the upstream V8 fix also restores correct wrapper invocation.
Credit is requested as: YMsora. https://github.com/YMs0ra
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