{"id":"GHSA-3vgf-8m4q-q4qr","summary":"vm2: Default VM can mutate host TypedArray and ArrayBuffer intrinsics after the host-prototype pollution fix","details":"## Summary\n\nvm2's current host-intrinsic prototype protection is incomplete. The fix for `GHSA-vwrp-x96c-mhwq` blocks sandbox writes into classic host intrinsics such as `Object.prototype`, `Array.prototype`, and `Function.prototype`, but current head still lets sandbox code in a default `VM` reach and mutate host `Uint8Array.prototype`, `%TypedArray%.prototype`, and `ArrayBuffer.prototype`.\n\nAfter `VM.run()` returns, normal host typed-array and ArrayBuffer objects observe attacker-controlled properties and methods installed by the sandbox.\n\n## Technical Details\n\nThe existing mitigation relies on `protectedHostObjects` in `lib/bridge.js`. That set is populated from `otherGlobalPrototypes`, which is built from a fixed inventory of classic globals:\n\n```js\nconst globalsList = [\n  'Number', 'String', 'Boolean', 'Date', 'RegExp', 'Map', 'WeakMap',\n  'Set', 'WeakSet', 'Promise', 'Function'\n];\n```\n\nThe inventory omits typed-array and ArrayBuffer intrinsics. Sandbox code can still reuse the host-prototype walking primitive from the prior public advisory:\n\n```js\nconst lookupGetter = ({}).__lookupGetter__;\nconst apply = Buffer.apply;\nconst protoGetter = apply.apply(lookupGetter, [Buffer, ['__proto__']]);\nconst hostBuffer = Buffer.from([1]);\n\nconst hostBufferPrototype = protoGetter.call(hostBuffer);\nconst hostUint8ArrayPrototype = protoGetter.call(hostBufferPrototype);\nconst hostTypedArrayPrototype = protoGetter.call(hostUint8ArrayPrototype);\nconst hostArrayBufferPrototype = protoGetter.call(hostBuffer.buffer);\n```\n\nThose objects are not sandbox-local. Inside the sandbox, `hostUint8ArrayPrototype === Uint8Array.prototype`, `hostTypedArrayPrototype === Object.getPrototypeOf(Uint8Array.prototype)`, and `hostArrayBufferPrototype === ArrayBuffer.prototype` are all false. Because the objects are not in `protectedHostObjects`, bridge `defineProperty` writes are forwarded into the real host objects.\n\nThis is the same guard-coverage boundary as the previous host-intrinsic prototype pollution fix, but with a missing intrinsic family. The bridge already has the correct enforcement shape; the protected inventory is too narrow.\n\n## PoC\n\nPoV: `poc/pov-host-typedarray-arraybuffer-prototype-pollution.js`\n\nCurrent-head output:\n\n```json\n{\n  \"status\": \"completed\",\n  \"vulnerable\": true,\n  \"node\": \"v25.8.0\",\n  \"v8\": \"14.1.146.11-node.20\",\n  \"control\": {\n    \"defineResult\": true,\n    \"sandboxReadsBack\": \"sandbox-only\",\n    \"hostControlAfter\": null\n  },\n  \"exploit\": {\n    \"hostUint8IsSandboxUint8\": false,\n    \"hostTypedArrayIsSandboxTypedArray\": false,\n    \"hostArrayBufferIsSandboxArrayBuffer\": false,\n    \"defineUint8\": true,\n    \"defineTypedArray\": true,\n    \"defineArrayBuffer\": true,\n    \"defineMethod\": true\n  },\n  \"hostEffect\": {\n    \"uint8Marker\": \"polluted-host-uint8array-prototype\",\n    \"typedArrayMarker\": \"polluted-host-typedarray-prototype\",\n    \"arrayBufferMarker\": \"polluted-host-arraybuffer-prototype\",\n    \"methodReturn\": \"sandbox-method-reached-host-uint8array\"\n  }\n}\n```\n\nThe control proves sandbox-local `Uint8Array.prototype` writes remain sandbox-local. The exploit path reaches host prototypes through the bridge and causes host-created objects to observe sandbox-installed properties after `VM.run()` returns.\n\n## Impact\n\nThis is a sandbox boundary violation and host intrinsic prototype pollution. An attacker who can run JavaScript in a default vm2 `VM` can mutate shared host typed-array and ArrayBuffer behavior without `NodeVM`, `require`, wildcard builtins, `nesting: true`, or any host-provided typed-array object.\n\nThe supplied PoV demonstrates integrity and availability impact by installing markers and a method on host prototypes:\n\n- `Uint8Array.prototype`\n- `%TypedArray%.prototype`, which affects typed-array families through the shared typed-array prototype chain\n- `ArrayBuffer.prototype`\n\nThe PoV does not claim direct host command execution or direct confidentiality impact. It is local-only and restores touched descriptors before exit.\n\n## Suggested Fix\n\nExtend the protected host-object inventory and identity/prototype mappings to typed-array and binary-data intrinsics, including at least:\n\n- `%TypedArray%.prototype`\n- `ArrayBuffer.prototype`\n- `SharedArrayBuffer.prototype` when present\n- `DataView.prototype`\n- all concrete typed-array prototypes present in the runtime, including `Uint8Array.prototype`, `Uint8ClampedArray.prototype`, `Int8Array.prototype`, `Uint16Array.prototype`, `Int16Array.prototype`, `Uint32Array.prototype`, `Int32Array.prototype`, `Float16Array.prototype` when present, `Float32Array.prototype`, `Float64Array.prototype`, `BigInt64Array.prototype`, and `BigUint64Array.prototype`\n\nA temporary patched-control that added this intrinsic family to `thisGlobalPrototypes` caused the same PoV's `Reflect.defineProperty()` calls to throw `VMError: Operation not allowed on contextified object`, and no host markers were installed.\n\nThe fix should cover the same host mutation traps used by the existing host-intrinsic protection: `set`, `defineProperty`, `deleteProperty`, and `preventExtensions`. It should not special-case `Buffer`; `Buffer` is only one way to reach the omitted host prototypes.\n\n## Affected Package/Versions\n\nConfirmed on current head `7a1f5100b96f48d34e0fe104ab37c0acc5944f92` / `v3.11.5` with Node `v25.8.0` / V8 `14.1.146.11-node.20`.\n\nConfirmed affected after the prior patch: `npm:vm2 \u003e= 3.11.0, \u003c= 3.11.5`.\n\nLocal sweep also reproduces on `v3.10.0` through `v3.10.5`, but that range overlaps the already-published `GHSA-vwrp-x96c-mhwq` range. `v3.9.0` through `v3.9.2` did not produce host-visible pollution in the same local test.\n\n## Why This Is Not Intended Behavior\n\nvm2 documents `VM` as a sandbox for untrusted code without `require`, with only JavaScript built-ins and Node's `Buffer` available by default. The known escape hatches do not explain this issue:\n\n- `require.builtin: ['*']` is a `NodeVM` configuration; this PoV uses default `VM`.\n- `nesting: true` is not enabled or used.\n- The README timeout caveat covers host code operating on objects returned from the sandbox; this PoV mutates host intrinsics and later affects ordinary host-created typed arrays and ArrayBuffers.\n\nThe project's own attack notes state that host-realm intrinsic prototypes should be protected from sandbox writes, while non-intrinsic host objects may remain mutable when intentionally exposed. Typed-array and ArrayBuffer prototypes are host intrinsics, not embedder-owned application objects.\n\n`Buffer` availability explains how the PoV reaches the host prototype chain, but it does not authorize mutation of unrelated host-realm intrinsics. The host effects are observed on new host-created typed arrays and ArrayBuffers after `VM.run()` returns; the host is not invoking an object returned from the sandbox.","aliases":["CVE-2026-92953"],"modified":"2026-10-05T23:00:06.309865725Z","published":"2026-10-05T22:45:22Z","database_specific":{"cwe_ids":["CWE-1321","CWE-913"],"severity":"CRITICAL","github_reviewed":true,"github_reviewed_at":"2026-10-05T22:45:22Z","nvd_published_at":null},"references":[{"type":"WEB","url":"https://github.com/patriksimek/vm2/security/advisories/GHSA-3vgf-8m4q-q4qr"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-92953"},{"type":"WEB","url":"https://github.com/patriksimek/vm2/commit/92a10fca7b3ca63bb1574b6795540264f6805b30"},{"type":"PACKAGE","url":"https://github.com/patriksimek/vm2"},{"type":"WEB","url":"https://github.com/patriksimek/vm2/releases/tag/v3.11.8"},{"type":"WEB","url":"https://www.vulncheck.com/advisories/vm2-3.11.0-through-3.11.7-prototype-pollution-via-typedarray"}],"affected":[{"package":{"name":"vm2","ecosystem":"npm","purl":"pkg:npm/vm2"},"ranges":[{"type":"SEMVER","events":[{"introduced":"3.11.0"},{"fixed":"3.11.8"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 3.11.7","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-3vgf-8m4q-q4qr/GHSA-3vgf-8m4q-q4qr.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H"}]}