GHSA-Q3FM-4WCW-G57X
Vulnerability from github – Published: 2026-05-29 17:38 – Updated: 2026-05-29 17:38Summary
defaultSandboxPrepareStackTrace in lib/setup-sandbox.js (lines 605, 607) appends to a fresh sandbox-realm lines = [] via lines[lines.length] = value. This is the exact invariant-violating pattern that GHSA-9qj6-qjgg-37qq (commit ca195f0, 2026-05-01) just patched in neutralizeArraySpeciesBatch and codified as Defense Invariant #11 ("Bridge-internal containers must not invoke sandbox code"). A sandbox-installed Array.prototype[N] setter fires during the bridge's safe-default stack-trace formatting and observes / intercepts each appended line.
Details
The post-9qj6 audit note in docs/ATTACKS.md (line 2111) states:
Equivalent pattern elsewhere in the bridge: audited; thisFromOtherArguments, otherFromThisArguments, and every other index-write site already use thisReflectDefineProperty or otherReflectDefineProperty. neutralizeArraySpeciesBatch was the lone outlier.
The audit is scoped to lib/bridge.js. lib/setup-sandbox.js was not covered. defaultSandboxPrepareStackTrace (added under post-#563 hardening for GHSA-v27g) constructs a sandbox-realm [header] array and appends each frame via the prototype-walking index assignment:
// lib/setup-sandbox.js, lines 601-610
const lines = [header];
for (let i = 0; i < callSites.length; i++) {
try {
lines[lines.length] = ' at ' + callSites[i];
} catch (e) {
lines[lines.length] = ' at <error formatting frame>';
}
}
return lines.join('\n');
This function runs every time sandbox code reads error.stack (or any path that triggers Error.prepareStackTrace). At the time it runs, user code has already had the opportunity to install a setter on Array.prototype[N]. Because lines starts at length 1, the first iteration writes index 1; if lines[1] has no own data property, V8 walks the prototype chain and invokes the sandbox-controlled setter.
The currently-assigned value is the string ' at ' + callSites[i] (the wrapped CallSite class's safe toString() returns 'CallSite {}'), which limits the immediate impact to a side channel, not an RCE pivot. The concern is structural rather than exploit-today:
- The just-codified Defense Invariant #11 explicitly requires that any list, set, or map allocated for the bridge's exclusive use must read and write through identity-stable, prototype-bypassing primitives. This site does not.
- The
catchbranch at line 607 also uses the same pattern, so a sandbox getter that throws oncallSites[i]access still routes its retry write through the prototype chain. - A future change that makes the appended slot value an object holding a host-realm reference (for example, an enriched frame record) would re-introduce the exact GHSA-9qj6 attack shape against this codepath.
The fix is mechanical and mirrors the GHSA-9qj6 patch: install entries via localReflectDefineProperty so each appended slot is an own data property and the prototype-chain setter is bypassed.
// Suggested patch (sketch)
let linesLen = 1;
function append(s) {
localReflectDefineProperty(lines, linesLen, {
__proto__: null,
value: s,
writable: true,
enumerable: true,
configurable: true,
});
linesLen++;
}
for (let i = 0; i < callSites.length; i++) {
try {
append(' at ' + callSites[i]);
} catch (e) {
append(' at <error formatting frame>');
}
}
The same pattern at callSiteGetters[callSiteGetters.length] = {...} (line 649) runs only at sandbox setup, before user code can install setters, so it is safe today. Converting it for symmetry would be cheap and forward-compatible.
PoC
vm2 v3.11.2, Node v24.
const { VM } = require('vm2');
const result = new VM().run(`
var observed = { setterFired: false, capturedValue: null, indexFired: null };
Object.defineProperty(Array.prototype, 1, {
configurable: true,
set(value) {
observed.setterFired = true;
observed.indexFired = 1;
observed.capturedValue =
typeof value === 'string' ? value.slice(0, 40) : typeof value;
},
get() { return undefined; }
});
var e = new Error('x');
e.stack;
observed;
`);
console.log(result);
// {
// setterFired: true,
// capturedValue: ' at CallSite {}',
// indexFired: 1
// }
Sandbox code observed and intercepted the bridge-internal write to lines[1]. Repeating the PoC with the setter installed at multiple indices (0, 1, 2, ...) captures every frame the formatter would otherwise return.
Impact
Hardening / Defense Invariant #11 violation. No direct sandbox escape on the current codebase: the value passed to the setter is a primitive string after the wrapped CallSite.toString(), so attacker-controlled code does not gain a host-realm reference from the setter argument alone. The GHSA-9qj6 entry's "Considered Attack Surfaces" note states the audit covered lib/bridge.js index-write sites; this filing reports the equivalent pattern in lib/setup-sandbox.js so the invariant is uniform across the bridge boundary and future enrichments of the appended record cannot regress into the GHSA-9qj6 shape.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 3.11.3"
},
"package": {
"ecosystem": "npm",
"name": "vm2"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.11.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-693"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-29T17:38:33Z",
"nvd_published_at": null,
"severity": "LOW"
},
"details": "## Summary\n\n`defaultSandboxPrepareStackTrace` in `lib/setup-sandbox.js` (lines 605, 607) appends to a fresh sandbox-realm `lines = []` via `lines[lines.length] = value`. This is the exact invariant-violating pattern that GHSA-9qj6-qjgg-37qq (commit ca195f0, 2026-05-01) just patched in `neutralizeArraySpeciesBatch` and codified as Defense Invariant #11 (\"Bridge-internal containers must not invoke sandbox code\"). A sandbox-installed `Array.prototype[N]` setter fires during the bridge\u0027s safe-default stack-trace formatting and observes / intercepts each appended line.\n\n## Details\n\nThe post-9qj6 audit note in `docs/ATTACKS.md` (line 2111) states:\n\n\u003e Equivalent pattern elsewhere in the bridge: audited; thisFromOtherArguments, otherFromThisArguments, and every other index-write site already use thisReflectDefineProperty or otherReflectDefineProperty. neutralizeArraySpeciesBatch was the lone outlier.\n\nThe audit is scoped to `lib/bridge.js`. `lib/setup-sandbox.js` was not covered. `defaultSandboxPrepareStackTrace` (added under post-#563 hardening for GHSA-v27g) constructs a sandbox-realm `[header]` array and appends each frame via the prototype-walking index assignment:\n\n```\n// lib/setup-sandbox.js, lines 601-610\nconst lines = [header];\nfor (let i = 0; i \u003c callSites.length; i++) {\n try {\n lines[lines.length] = \u0027 at \u0027 + callSites[i];\n } catch (e) {\n lines[lines.length] = \u0027 at \u003cerror formatting frame\u003e\u0027;\n }\n}\nreturn lines.join(\u0027\\n\u0027);\n```\n\nThis function runs every time sandbox code reads `error.stack` (or any path that triggers `Error.prepareStackTrace`). At the time it runs, user code has already had the opportunity to install a setter on `Array.prototype[N]`. Because `lines` starts at length 1, the first iteration writes index 1; if `lines[1]` has no own data property, V8 walks the prototype chain and invokes the sandbox-controlled setter.\n\nThe currently-assigned value is the string `\u0027 at \u0027 + callSites[i]` (the wrapped `CallSite` class\u0027s safe `toString()` returns `\u0027CallSite {}\u0027`), which limits the immediate impact to a side channel, not an RCE pivot. The concern is structural rather than exploit-today:\n\n- The just-codified Defense Invariant #11 explicitly requires that any list, set, or map allocated for the bridge\u0027s exclusive use must read and write through identity-stable, prototype-bypassing primitives. This site does not.\n- The `catch` branch at line 607 also uses the same pattern, so a sandbox getter that throws on `callSites[i]` access still routes its retry write through the prototype chain.\n- A future change that makes the appended slot value an object holding a host-realm reference (for example, an enriched frame record) would re-introduce the exact GHSA-9qj6 attack shape against this codepath.\n\nThe fix is mechanical and mirrors the GHSA-9qj6 patch: install entries via `localReflectDefineProperty` so each appended slot is an own data property and the prototype-chain setter is bypassed.\n\n```javascript\n// Suggested patch (sketch)\nlet linesLen = 1;\nfunction append(s) {\n localReflectDefineProperty(lines, linesLen, {\n __proto__: null,\n value: s,\n writable: true,\n enumerable: true,\n configurable: true,\n });\n linesLen++;\n}\nfor (let i = 0; i \u003c callSites.length; i++) {\n try {\n append(\u0027 at \u0027 + callSites[i]);\n } catch (e) {\n append(\u0027 at \u003cerror formatting frame\u003e\u0027);\n }\n}\n```\n\nThe same pattern at `callSiteGetters[callSiteGetters.length] = {...}` (line 649) runs only at sandbox setup, before user code can install setters, so it is safe today. Converting it for symmetry would be cheap and forward-compatible.\n\n## PoC\n\nvm2 v3.11.2, Node v24.\n\n```javascript\nconst { VM } = require(\u0027vm2\u0027);\nconst result = new VM().run(`\n var observed = { setterFired: false, capturedValue: null, indexFired: null };\n Object.defineProperty(Array.prototype, 1, {\n configurable: true,\n set(value) {\n observed.setterFired = true;\n observed.indexFired = 1;\n observed.capturedValue =\n typeof value === \u0027string\u0027 ? value.slice(0, 40) : typeof value;\n },\n get() { return undefined; }\n });\n var e = new Error(\u0027x\u0027);\n e.stack;\n observed;\n`);\nconsole.log(result);\n// {\n// setterFired: true,\n// capturedValue: \u0027 at CallSite {}\u0027,\n// indexFired: 1\n// }\n```\n\nSandbox code observed and intercepted the bridge-internal write to `lines[1]`. Repeating the PoC with the setter installed at multiple indices (0, 1, 2, ...) captures every frame the formatter would otherwise return.\n\n## Impact\n\nHardening / Defense Invariant #11 violation. No direct sandbox escape on the current codebase: the value passed to the setter is a primitive string after the wrapped `CallSite.toString()`, so attacker-controlled code does not gain a host-realm reference from the setter argument alone. The GHSA-9qj6 entry\u0027s \"Considered Attack Surfaces\" note states the audit covered `lib/bridge.js` index-write sites; this filing reports the equivalent pattern in `lib/setup-sandbox.js` so the invariant is uniform across the bridge boundary and future enrichments of the appended record cannot regress into the GHSA-9qj6 shape.",
"id": "GHSA-q3fm-4wcw-g57x",
"modified": "2026-05-29T17:38:33Z",
"published": "2026-05-29T17:38:33Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/patriksimek/vm2/security/advisories/GHSA-q3fm-4wcw-g57x"
},
{
"type": "WEB",
"url": "https://github.com/patriksimek/vm2/commit/ad31adc1fc4a2c163f2f8c11ab4af206074528fd"
},
{
"type": "PACKAGE",
"url": "https://github.com/patriksimek/vm2"
},
{
"type": "WEB",
"url": "https://github.com/patriksimek/vm2/releases/tag/v3.11.4"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N",
"type": "CVSS_V4"
}
],
"summary": "vm2 setup-sandbox.js violates Defense Invariant #11 in stack-trace formatter"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
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