GHSA-9v7c-q64q-vv33 Nuxt: Dot segments in the request path bypass `server/middleware` path checks and server route rules on page routes

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

Summary Since `4.6.0`, Nuxt resolves `.` and `..` segments in the request path, including percent-encoded forms such as `%2e`, before rendering a page. Nitro's routing, Nitro's route rules and `server/middleware` see the path with those segments still in place. A request for `/%2e/admin` therefore renders the page at `/admin`, while server-side checks keyed on `/admin` do not apply. Impact An unauthenticated attacker can bypass server-side controls that match on the request path of a page route. `server/middleware` that checks `event.path` (or `event.node.req.url`) is skipped: ```ts export default defineEventHandler((event) => { if (event.path.startsWith('/admin') && !isAuthenticated(event)) { throw createError({ statusCode: 401 }) } }) ``` With this middleware, `/admin` returns 401, but `/%2e/admin`, `/.%2e/admin` and `/x/%2e%2e/admin` reach the middleware with `event.path` set to `/./admin`, `/../admin` and `/x/../admin`, and render `app/pages/admin.vue` along with the data it fetches during server rendering. Server-side `redirect` and `headers` route rules are skipped in the same way, so `'/admin/**': { redirect: '/login' }` does not redirect `/%2e/admin/secret`, and per-route security headers such as `Content-Security-Policy` are not sent. Not affected: • API handlers in `server/api` and `server/routes`. Nitro's router does not resolve dot segments, so these requests do not reach the handler. • `appMiddleware` route rules and middleware declared with `definePageMeta`, which are matched against the resolved route. • Nuxt `3.x` and `4.0.0` to `4.5.x`, which pass the path to the page router unchanged, so these requests 404. Browsers resolve dot segments before sending a request, so exploitation requires a client that sends the path as written. Patches Fixed in `[email protected]` and `@nuxt/[email protected]`. A page request whose path contains `.` or `..` segments now receives a 404 instead of rendering the page the path resolves to, and route-rule keys and lookup paths have their dot segments resolved, including percent-encoded spellings, before they are compared. Workarounds Reject dot segments in a server middleware that runs before your other middleware (middleware runs in file name order): ```ts // server/middleware/0.dot-segments.ts export default defineEventHandler((event) => { if (/(?:^|\/)\.{1,2}(?:\/|$)/.test(event.path.split('?')[0])) { throw createError({ statusCode: 404 }) } }) ``` Checking `getRequestURL(event).pathname` instead of `event.path` is not a sufficient workaround: it resolves dot segments, but keeps percent-encoding such as `%61` that the page router decodes. Path checks in server middleware should also account for the page router matching paths case-insensitively unless `router.options.sensitive` is set. A reverse proxy or CDN that normalises the request path before forwarding it also removes the mismatch. Credits Thanks to @vinzabe, @nikhilagrawalsf (Nikhil Agrawal, Mettle Labs), @0xjunwei and @kq5y, who reported this issue independently.