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.
Weakness
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Potential Mitigations
- Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
- Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
- One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
References
- 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/security/advisories/GHSA-5h3f-q97h-ccvc
- https://www.vulncheck.com/advisories/vm2-before-3.12.2-authorization-bypass-via-custom-resolver