CVE-2026-88009

## Summary Traefik accepts an HTTP/1.x request whose request-target is in rootless / opaque form (for example `GET http:http://internal-vhost/admin HTTP/1.1`). Go parses this into `URL.Opaque` with an empty `URL.Path`, so Traefik evaluates all routing, path-sanitization, middleware and access-log decisions against a path that normalizes to `/`, while the proxy forwards the attacker's original target byte-for-byte to the backend. Router path/prefix guards, `forwardAuth` path-scoped policies and the `encodedCharacters` hardening never see the real target, and the access log records every such request as `GET / HTTP/1.1`. Against a backend that resolves a rootless target as a path, this yields cross-vhost routing bypass, path-scoped authorization bypass and access-log evasion — unauthenticated, with stock entrypoint defaults. Traefik v3.0 through v3.6 are end-of-life and are also affected; they will not receive a fix on their own line. Users on those versions must upgrade to v3.7.13. ## Patches - https://github.com/traefik/traefik/releases/tag/v2.11.57 - https://github.com/traefik/traefik/releases/tag/v3.7.13 ## For more information If you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues). <details> <summary>Original Description</summary> ## Summary The scanner claims `rewriteRequestBuilder` (`pkg/proxy/httputil/proxy.go:97`) rebuilds the outbound target from `URL.Path` / `RawPath` / `RawQuery` but never clears `URL.Opaque`, so a client sending a rootless request-target (`GET http:http://internal-vhost/admin HTTP/1.1`) has that byte string written verbatim into the backend request line while Traefik routes, sanitizes, guards and logs an empty path. **The claim is correct in every load-bearing detail, and it reproduces end to end on the GA image `traefik:v3.7` (v3.7.9, go1.26.5) with stock entrypoint defaults.** Three separate consequences were observed on the wire, not inferred: 1. **Cross-v