CVE-2026-84373: Vitest: Path Traversal / Arbitrary File Read via @vitest/mocker Redirect Mock

@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).