GHSA-7q3f-wx44-378m

## Summary

`isPathAllowedForModule` decides whether a resolved path belongs to an allowlisted external module using a raw string prefix test. `node_modules/foo2` starts with `node_modules/foo`, so a package whose name merely shares a prefix with an allowlisted one is treated as being inside it, and a relative require from the allowlisted package reaches it even with transitive loading disabled.

## Where it is

`lib/resolver-compat.js`, lines 122 to 132, quoted from HEAD `7a1f5100b96f48d34e0fe104ab37c0acc5944f92`:

```js isPathAllowedForModule(path, mod) { if (!super.isPathAllowed(path)) return false; if (mod) { if (mod.allowTransitive) return true; if (path.startsWith(mod.path)) { const rem = path.slice(mod.path.length); if (!/(?:^|[\\/])node_modules(?:$|[\\/])/.test(rem)) return true; } } return this.externals.some(regex => regex.test(path)); } ```

With `mod.path` of `.../node_modules/foo` and a resolved path of `.../node_modules/foo2/index.js`, `startsWith` is true and `rem` is `2/index.js`, which contains no `node_modules` segment, so the function returns true.

The `node_modules` test in `rem` is what stops a genuine transitive dependency from slipping through. It does not stop a sibling, because a sibling's remainder never contains that segment.

## Impact

Code running in `NodeVM` under an external module allowlist with `transitive: false` can reach a package that was not allowlisted, provided an allowlisted package performs a relative require to a prefix-sharing sibling.

Two preconditions are worth stating plainly rather than leaving implicit. The deployment must already have such a package layout, and an allowlisted package must have a reachable code path that does the relative require. This is not something the attacker creates; it is something they find. That narrows it considerably, and it is why I have not scored it higher.

## Reachability

`NodeVM.run` at `lib/nodevm.js:506` executes the script. `require` comes from `createRequireForModule` at `lib/setup-node-sandbox.js:168-172` and reaches the resolver callback at `lib/nodevm.js:380-384`. `LegacyResolver.resolveFull` at `lib/resolver-compat.js:145-160` sets `currMod` for direct requires, the relative specifier resolves through `DefaultResolver.resolveFull` and `tryFile` at `lib/resolver.js:327-330`, and the authorization decision lands on the function above.

## Suggested fix

Require a separator after the prefix, so a sibling cannot match:

```js if (path === mod.path || path.startsWith(mod.path + path.sep)) { ```

That is the same anchoring the `rem` regex already applies to `node_modules`, applied one level earlier.