# vm2 timeout option bypass via FinalizationRegistry cleanup callback

Source: https://junglewise.ai/threats/duplicate-advisory-vm2-timeout-option-bypass-via-finalizationregistry-19556987  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-17. Updated: 2026-10-05  
License: CC BY 4.0 with a link back

Severity: high · CVSS 7.5 · Published 2026-09-17

vm2 is a library that sandboxes JavaScript code execution with configurable resource limits, including timeout enforcement. This vulnerability allows sandboxed code to bypass the timeout protection by registering a FinalizationRegistry callback that executes outside the timeout accounting when the garbage collector later runs, enabling a denial-of-service attack that blocks the host event loop indefinitely.

Technologies: [vm2 (npm)](https://junglewise.ai/threats/technologies/vm2), [Vm2](https://junglewise.ai/threats/technologies/x-vm2). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** High severity, with a CVSS score of 7.5, published 17 September 2026.

**Which products and versions are affected?** vm2 (npm) <= 3.11.6; Vm2 <= 3.11.6.

**Is there a fix for This vulnerability?** Yes: fixed in 3.11.7. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run vm2 (npm) or Vm2 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 3.11.7

## Technical details

The vulnerability exists because vm2's timeout enforcement wraps only the synchronous VM#run() call but not asynchronous callbacks triggered by the V8 garbage collector. FinalizationRegistry and WeakRef are exposed unmodified to sandboxed code and not hardened, allowing an attacker to register a cleanup callback that executes outside any timeout protection when an object is garbage collected. A malicious cleanup callback can then execute a busy loop, causing denial of service by blocking the host event loop indefinitely.

## Affected products

- vm2 <= 3.11.6

## Timeline

- 2026-08-24: disclosed
- 2026-09-17: advisory
- 2026-10-05: other: Advisory withdrawn as duplicate of GHSA-r4fx-v8hh-22mv

## References

- [https://github.com/patriksimek/vm2/security/advisories/GHSA-r4fx-v8hh-22mv](https://github.com/patriksimek/vm2/security/advisories/GHSA-r4fx-v8hh-22mv)

## Related threats

- [vm2 NodeVM path bypass in custom resolution](https://junglewise.ai/threats/duplicate-advisory-vm2-nodevm-custom-resolution-bypasses-external-path-5d3a7272)
- [vm2 NodeVM zlib buffer pool information disclosure](https://junglewise.ai/threats/duplicate-advisory-vm2-nodevm-zlib-buffers-expose-pooled-host-memory-6007c734)
- [vm2 host Promise rejection denial of service in construct trap](https://junglewise.ai/threats/duplicate-advisory-vm2-host-promise-rejection-from-an-exposed-f7aba6ba)
- [vm2 sandbox escape via Buffer backing-store ownership bypass](https://junglewise.ai/threats/cve-2026-100723-vm2-before-3-12-2-does-not-apply-its-buffer-backing-store)
- [vm2 unhandled Promise rejection in construct trap](https://junglewise.ai/threats/cve-2026-100722-vm2-before-3-12-2-does-not-apply-host-side-promise-rejection)