PT-2026-38396 · Npm · Vm2
Published
2026-05-07
·
Updated
2026-05-07
·
CVE-2026-44005
CVSS v3.1
10
Critical
| Vector | AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H |
Summary
vm2's bridge exposes mutable proxies for real host-realm intrinsic prototypes and then forwards sandbox writes into the underlying host objects with otherReflectSet() and otherReflectDefineProperty(), which lets attacker-controlled JavaScript running in a default VM or inherited NodeVM mutate shared host Object.prototype, Array.prototype, and Function.prototype from inside the sandbox.
Details
BaseHandler.apply() unwraps sandbox-controlled receivers and arguments with otherFromThis() / otherFromThisArguments() and then directly invokes the real host function with ret = otherReflectApply(object, context, args), so any default-exposed host function that can surface a prototype getter becomes a prototype-walking primitive (lib/bridge.js:665-676). BaseHandler.get() special-cases proto and returns the host-side descriptor or proxy target prototype, which is enough for the attacker to reuse the host lookupGetter (' proto ') accessor repeatedly until the walk lands on host Object.prototype, Array.prototype, or Function.prototype (lib/bridge.js:590-616). Once the attacker has a proxy to a host intrinsic prototype, BaseHandler.set() performs value = otherFromThis(value); return otherReflectSet(object, key, value) === true;, which writes attacker-controlled data directly into the shared host object instead of keeping the mutation sandbox-local; BaseHandler.defineProperty() repeats the same design at otherReflectDefineProperty(object, prop, otherDesc) for descriptor-based writes (lib/bridge.js:641-649, lib/bridge.js:753-774). Existing validation does not stop the attack because the constructor filter only blocks one dangerous-property access pattern, setPrototypeOf() only blocks prototype replacement rather than ordinary property assignment, and containsDangerousConstructor() only protects one later re-unwrapping path instead of the initial host-prototype write sink (lib/bridge.js:494-530, lib/bridge.js:595-610, lib/bridge.js:660-662).
PoC
Run the following code snippet and observe that the value of vm2EscapeMarker is polluted:
const { VM } = require('vm2');
const vm = new VM();
vm.run(`
const g = ({}). lookupGetter ;
const a = Buffer.apply;
const p = a.apply(g, [Buffer, [' proto ']]);
const hostObjectProto = p.call(p.call(p.call(p.call(Buffer.of()))));
hostObjectProto.vm2EscapeMarker = 'polluted-object-prototype';
`);
console.log({}.vm2EscapeMarker)Impact
Sandbox escape and prototype pollution.
Fix
Prototype Pollution
Code Injection
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Related Identifiers
Affected Products
Vm2