GHSA-82fw-gwwq-j7x9

## Summary `@vitest/mocker` registers a redirect mock's target path without validating it against the dev server's file-serving allowlist. An attacker who can reach the dev server's WebSocket can register a redirect mock pointing outside the project root; when the mocked module is requested, the plugin's `load` hook returns `readFile(<attacker path>)` as the module source, disclosing local files.

This is exploitable **without authentication** only through the public `mockerPlugin` / standalone `interceptorPlugin` exports (used by third-party dev servers), which register the handler on Vite's unauthenticated HMR socket. Vitest's own browser mode registers mocks over a **token-authenticated** RPC and is not remotely reachable by default (see Scope).

## Affected code `packages/mocker/src/node/interceptorPlugin.ts`.

The `load` hook is the file-read sink:

```ts if (mock.type === 'redirect') { return readFile(mock.redirect, 'utf-8') } ```

`mock.redirect` is derived from client input at registration time with no boundary check:

```ts if (event.type === 'redirect') { const redirectUrl = new URL(event.redirect) event.redirect = join(server.config.root, redirectUrl.pathname) } registry.register(event) ```

There is no `server.fs.allow` / `server.fs.deny` check and no assertion that the resolved path stays within the project root.

## Registration paths and trust boundaries - **Public `mockerPlugin` / `interceptorPlugin` (unauthenticated).** In `configureServer`, the plugin registers `server.ws.on('vitest:interceptor:register', …)` on Vite's HMR WebSocket. That socket performs no token, Origin, or same-origin check, so any client that can reach it can register a redirect mock. This is the path the "unauthenticated" impact applies to. - **Vitest browser mode (authenticated).** Mocks register over the browser RPC (`registerMock`), which sits behind a per-run token (`isValidApiRequest`, a random `api.token`). The interceptor's `configureServer` socket is not used for registration here (in v5 it does not run at all, as the plugin is injected per environment). The same missing boundary check exists on the authenticated RPC path, but reaching it requires the token, so it is not a remote-unauthenticated read.

## Path handling `new URL(redirect).pathname` combined with `join(root, pathname)` does **not** confine reads to the root:

- Special/hierarchical schemes (`file:`, `http:`) are normalized by WHATWG URL, so `..` segments are collapsed and the result stays under the root. Payloads of the form `file:///../../etc/passwd` do **not** escape. - A non-special (opaque) scheme preserves `..` in `pathname`, so `join(root, "../../…/etc/passwd")` resolves outside the root and reads an arbitrary file.

Even without escaping the root, the missing `server.fs` check allows reading any in-root file the dev server would otherwise refuse to serve (for example an in-root `.env` or source that is denied by `server.fs.deny`).

## Scope / preconditions - This is a **development-server** issue. The dev server binds to `localhost` by default and is not reachable from the network unless the developer exposes it (`server.host` / `0.0.0.0`, a LAN bind, or a proxy). - A raw (non-browser) client against a reachable server bypasses browser origin and CORS protections entirely and can both register the mock and read the response. - A browser-based drive-by against a localhost server is substantially mitigated by Vite defaults: the default CORS origin allowlist is limited to `localhost` origins, and `server.allowedHosts` blocks DNS-rebinding, so a cross-origin page cannot read the file contents back.

## Impact Disclosure of local files readable by the dev-server process (source, in-root `.env`/secrets, and, via the opaque-scheme payload, files outside the project root). No integrity or availability impact.

## Affected versions Present since `@vitest/mocker` was introduced.

- **Affected: `@vitest/mocker` >= 2.1.0** (shipped in `vitest` and `@vitest/browser` >= 2.1.0), through 4.1.x and the 5.0.0 pre-releases. - **Fixed:** Vitest 4.1.11 and 5.0.0. Older majors (2.1.x, 3.x) are not maintained and are not planned to receive the fix.

## Fix Validate the resolved redirect target against Vite's file-serving allowlist (`isFileLoadingAllowed`) before registering it, at every registration site, and stop registering the interceptor WebSocket events in Vitest's browser mode (mocks there flow through the authenticated RPC).