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bdu:2026-11278

2026-10-07T09:38:13.486327+00:00

bdu:2026-11278

EUVD-2026-349333

2026-10-07T09:38:13.486370+00:00

EUVD-2026-349333

fkie_cve-2026-71324

2026-10-07T09:38:13.486392+00:00

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.53, 3.6.24, and 3.7.9, Traefik's default HTTP reverse proxy forwards a plain HTTP/2 or HTTP/3 CONNECT request and its body to an HTTP/1.1 upstream through a shared net/http.Transport. When the upstream answers the CONNECT with a keep-alive non-2xx response and does not drain the body, Traefik returns the desynchronized backend socket to its shared pool and reuses it for other clients. An unauthenticated attacker can use this behavior to make a different client read the attacker's smuggled response, which can include authenticated or private content from another request. The ForwardAuth middleware with forwardBody true and preserveRequestMethod true can re-issue a CONNECT with the buffered body attached, exposing the auth-client pool to the same desynchronization. This issue is fixed in 2.11.53, 3.6.24, and 3.7.9.

GHSA-3ccp-42pg-hgv6 — Traefik: Cross-user response poisoning via proxied CONNECT on Traefik's shared backend keep-alive pool

2026-10-07T09:38:13.486443+00:00

Affected: Go: github.com/traefik/traefik/v2, Go: github.com/traefik/traefik/v3, Go: github.com/traefik/traefik

## Summary

There is a critical vulnerability in Traefik's default HTTP reverse proxy that leads to unauthenticated cross-user response poisoning. When a client opens an HTTP/2 or HTTP/3 `CONNECT` request, Traefik forwards it — body included — to an HTTP/1.1 upstream over a shared `net/http.Transport`. If the upstream answers the CONNECT with a keep-alive non-2xx response without draining the body, the now-desynchronized backend socket is returned to Traefik's shared connection pool and reused for other clients, letting an attacker make a different client read a response the attacker smuggled — which may be another user's authenticated or private content. The entrypoint's `sanitizePath` option (default `true`) is not a reliable defense: backends that answer `CONNECT /` with a keep-alive non-2xx remain exploitable. The experimental FastProxy implementation was not affected. The issue is fixed by deferring the forwarded CONNECT payload until the backend accepts the tunnel, by not returning CONNECT connections to the shared idle pool, and by discarding the CONNECT body in the ForwardAuth path.

## Patches

- https://github.com/traefik/traefik/releases/tag/v2.11.53 - https://github.com/traefik/traefik/releases/tag/v3.6.24 - https://github.com/traefik/traefik/releases/tag/v3.7.9

## For more information

If you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).

Original Description

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