vm2's Bridge Proxy set trap ignores receiver parameter, enabling host object property injection via prototype chain

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

EPSS

• CVE-2026-47209: 0.29% estimated exploitation activity in the next 30 days; percentile 21.34 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Vulnerable Code Impact Sandbox code can write arbitrary properties (including dangerous Symbol-keyed properties) to any host object it holds a reference to, by creating a prototype-inheriting child: Combined with the…

Published by the source

29 May 2026, 17:49 UTC

Last modified by the source

12 Jun 2026, 19:45 UTC

Source last checked

26 Oct 2026, 12:55 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c4cf-2hgv-2qv6

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-c4cf-2hgv-2qv6

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# Patch Next advisory brief: CVE-2026-47209

Advisory: vm2's Bridge Proxy set trap ignores receiver parameter, enabling host object property injection via prototype chain
IDs: CVE-2026-47209, GHSA-c4cf-2hgv-2qv6
Record: https://patchnext.com/advisories/cve-2026-47209 (revision 2, source checked 26 Oct 2026, 12:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: vm2 3.11.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm vm2: affected <= 3.11.3; fixed in 3.11.4

## Suggested inspection (read-only)
- `npm ls vm2 --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on vm2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-c4cf-2hgv-2qv6 (OSV record GHSA-c4cf-2hgv-2qv6 lists affected ranges: npm vm2 >=0 <3.11.4 (fixed))
- Verified: https://github.com/advisories/GHSA-c4cf-2hgv-2qv6 (GitHub-reviewed advisory GHSA-c4cf-2hgv-2qv6 lists affected ranges: npm vm2 >=0 <=3.11.3)

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