GHSA-q3fm-4wcw-g57x: Vm2 Vm2 Setup-sandbox.js Violates Defense Invariant Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q3fm-4wcw-g57x",
  "modified" : "2026-05-29T17:38:33Z",
  "published" : "2026-05-29T17:38:33Z",
  "aliases" : [ ],
  "summary" : "vm2 setup-sandbox.js violates Defense Invariant #11 in stack-trace formatter",
  "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's 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> 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 < callSites.length; i++) {\n    try {\n        lines[lines.length] = '    at ' + callSites[i];\n    } catch (e) {\n        lines[lines.length] = '    at <error formatting frame>';\n    }\n}\nreturn lines.join('\\n');\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 `'    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:\n\n- 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.\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 < callSites.length; i++) {\n    try {\n        append('    at ' + callSites[i]);\n    } catch (e) {\n        append('    at <error formatting frame>');\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('vm2');\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 === 'string' ? value.slice(0, 40) : typeof value;\n        },\n        get() { return undefined; }\n    });\n    var e = new Error('x');\n    e.stack;\n    observed;\n`);\nconsole.log(result);\n// {\n//   setterFired: true,\n//   capturedValue: '    at CallSite {}',\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'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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "vm2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.11.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.11.3"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-693" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-29T17:38:33Z",
    "nvd_published_at" : null
  }
}