vm2: NodeVM custom resolution bypasses external path boundaries

Why it is Amber

• CVSS 9.0 critical
• Remotely exploitable without logging in
• On your watchlist: npm

Affected packages

References

• https://github.com/advisories/GHSA-5h3f-q97h-ccvc
• https://github.com/patriksimek/vm2/security/advisories/GHSA-5h3f-q97h-ccvc
• https://nvd.nist.gov/vuln/detail/CVE-2026-100721
• https://github.com/patriksimek/vm2/commit/6ac3916da84e060c403e407b6b6318fcc66b0e72
• https://github.com/patriksimek/vm2/commit/91034466bfb7f56b95fd48083ec6ca36d058f164
• https://github.com/patriksimek/vm2/commit/ab4ee7d803e8c80155e9eb3672226bddbca4aa9c
• https://github.com/patriksimek/vm2/commit/fb4977f6211da6cadffdf1f3a2017a826a21c51f
• https://github.com/patriksimek/vm2/releases/tag/v3.12.2
• https://www.vulncheck.com/advisories/vm2-before-3.12.2-authorization-bypass-via-custom-resolver
• https://github.com/advisories/GHSA-5h3f-q97h-ccvc

Original description

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.