GHSA-3xf4-9g3c-4h4w Nuxt dev server exposes generated appSecret through Vite file serving

• npm @nuxt/vite-builder: >= 4.6.0, < 4.6.3 → fixed in 4.6.3

Impact When no `appSecret` is configured (via `NUXT_APP_SECRET`, `NITRO_APP_SECRET` or `runtimeConfig.appSecret`), `nuxt dev` generates a development secret and stores it in `/app-secret` (by default `.nuxt/app-secret`). The build directory is inside the directories that Nuxt passes to Vite's `server.fs.allow`, so the file can be fetched from the dev server: ```bash curl http:///_nuxt/@fs//.nuxt/app-secret ``` Anyone who can read it can compute every secret derived from it with `deriveSecret()`, including the default password used by `useSession`, and so can forge session cookies accepted by that dev server. Exploitation requires direct HTTP access to the dev server. `nuxt dev` listens on localhost by default, so this mainly affects dev servers that are exposed to a network (for example with `--host`, a published container port or a tunnel). A malicious website cannot read the file through a developer's browser: Vite's CORS and host checks prevent pages on other origins from reading the response. Production builds never generate an `appSecret` and are not affected. Dev servers with an explicitly configured `appSecret` do not use the generated file. Patches Fixed in `@nuxt/vite-builder` 4.6.3, which `nuxt` 4.6.3 depends on. The dev server now adds `app-secret` to Vite's `server.fs.deny`, keeping Vite's default deny list. Workarounds Set `NUXT_APP_SECRET` in `.env` to a random value of at least 32 characters (for example the output of `openssl rand -base64 32`), or avoid exposing the dev server to untrusted networks. If a dev server using a generated secret has been reachable by untrusted clients, delete `.nuxt/app-secret` (a new secret is generated on the next `nuxt dev`) or set `NUXT_APP_SECRET`. Either invalidates existing dev sessions.