Auth bypass in Patriksimek Vm2
CVE-2026-100721
vm2 before 3.12.2 contains an authorization bypass in the NodeVM external-module resolver. When an embedder configures `require.external` with a custom resolver (and `context: 'host'`), `LegacyResolver.customResolve` in lib/resolver-compat.js records the resolved module directory in `this.externals` as `new RegExp('^' + escapeRegExp(resolvedPath))`, without requiring a path separator or end-of-string boundary. Untrusted guest code can therefore require the allowlisted module (e.g. `foo`) and then require the absolute path of a non-allowlisted sibling whose path merely shares the resolved prefix (e.g. `.../node_modules/foo2/index.js`); the sibling passes `isPathAllowedForModule` and is loaded through `hostRequire`, so its top-level code runs in the host process before the exports are wrapped with `vm.readonly`, resulting in a sandbox escape and arbitrary code execution in the host context.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.006 (48.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 48.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002
Affected products
Weakness classification (CWE)
Public proof-of-concept exploits
References
- GitHub Security Advisory (GHSA-5h3f-q97h-ccvc) (vendor-advisory)
- Patch Commit (patch)
- Patch Commit (patch)
- Patch Commit (patch)
- VulnCheck Advisory: vm2 before 3.12.2 Authorization Bypass via Custom Resolver (third-party-advisory)
Frequently asked questions
- What is CVE-2026-100721?
- CVE-2026-100721 is a critical-severity vulnerability in Patriksimek Vm2, classified under Incorrect Authorization. CVSS score: 9.0/10. Published 2026-09-27.
- How severe is CVE-2026-100721?
- Critical severity. CVSS v3 base score is 9.0 out of 10.
- Is CVE-2026-100721 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.