Nitro is a next generation server toolkit. Prior to 3.0.260429-beta, an attacker could bypass a proxy route rule by sending percent-encoded path traversal (..%2f) in the URL, causing Nitro to forward a request that the upstream resolved outside the configured scope. This vulnerability is fixed in 3.0.260429-beta.

Affected: npm: nitro, npm: nitropack

A proxy route rule like:

```ts routeRules: { "/api/orders/**": { proxy: { to: "http://upstream/orders/**" } } } ```

is intended to limit the proxy to URLs under `/api/orders/`. Before the patch, an attacker could bypass that scope by sending percent-encoded path traversal (`..%2f`) in the URL, causing Nitro to forward a request that the upstream resolved outside the configured scope. Example exploit:

``` GET /api/orders/..%2fadmin%2fconfig.json ```

Nitro sees `..%2f` as opaque characters at match time, the `/api/orders/**` rule matched, and the raw path was forwarded to the upstream as `/orders/..%2fadmin/config.json`. An upstream that decodes `%2F` to `/` then resolved `..` and can serve `/admin/config.json` outside the intended scope.

### Are you affected?

Users may be affected if **ALL** of the following are true:

1. Their project uses Nitro's `routeRules` with a `proxy` entry (`{ proxy: { to: "..." } }`). 2. The proxy `to` value uses a `/**` wildcard suffix to forward sub-paths. 3. The **upstream** behind the proxy decodes `%2F` as `/` before routing or filesystem lookup. 4. Proxy route rules are _not_ handled natively at CDN (nitro v3 and vercel)

Whether the bypass actually leaks data depends on the upstream. Modern JS frameworks keep `%2F` opaque per RFC 3986 and are safe by construction.

- **Safe examples:** H3 v2, Express v5, Hono v4 — modern JS frameworks keep `%2F` opaque per RFC 3986. - **Vulnerable examples:** naive imlementations that decodes the UR…