vm2: NodeVM custom resolution bypasses external path boundaries

Exploitation

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

CVSS 4.0

9.5 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H · score source

EPSS

• CVE-2026-100721: 0.59% estimated exploitation activity in the next 30 days; percentile 48.30 (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 At source revision 91034466bfb7f56b95fd48083ec6ca36d058f164 of vm2 3.11.8, an untrusted NodeVM guest can turn one allowlisted custom-resolved module into authorization for a separate file whose path merely shares the resolved path's string prefix. LegacyResolver.customResolve stores the resolved path in this.externals as ^<path without an end or separator boundary; a later absolute require of a sibling such as foo2/index.js therefore passes the external check and is loaded through hostRequire when the configured context is host. The decisive attack loaded foo as FOOOK and then executed the prefix-sharing sibling, which returned PREFIXPWN after invoking childprocess; an otherwise identical control denied the sibling with ENOTFOUND. Technical Details The affected configuration is a documented NodeVM use in which the embedder sets require.external to {modules: ['foo'], transitive: false}, supplies a custom resolver that returns the foo directory, sets a root directory, and uses…

Published by the source

5 Oct 2026, 23:24 UTC

Last modified by the source

5 Oct 2026, 23:30 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5h3f-q97h-ccvc

2. Revision 3 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-5h3f-q97h-ccvc

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-5h3f-q97h-ccvc

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# Patch Next advisory brief: CVE-2026-100721

Advisory: vm2: NodeVM custom resolution bypasses external path boundaries
IDs: CVE-2026-100721, GHSA-5h3f-q97h-ccvc
Record: https://patchnext.com/advisories/cve-2026-100721 (revision 4, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: vm2 3.12.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm vm2: affected <= 3.12.1; fixed in 3.12.2

## 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://github.com/advisories/GHSA-5h3f-q97h-ccvc (GitHub-reviewed advisory GHSA-5h3f-q97h-ccvc lists affected ranges: npm vm2 >=0 <=3.12.1)
- Verified: https://osv.dev/vulnerability/GHSA-5h3f-q97h-ccvc (OSV record GHSA-5h3f-q97h-ccvc lists affected ranges: npm vm2 >=0 <3.12.2 (fixed))

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