Bug 2512342 (CVE-2026-71324)

Summary: CVE-2026-71324 github.com/traefik/traefik: Traefik: Information disclosure via response poisoning in shared backend pool
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: anjoseph, jprabhak, sdawley, wtam
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Traefik. Traefik's HTTP reverse proxy can improperly handle HTTP/2 or HTTP/3 CONNECT requests forwarded to an HTTP/1.1 upstream. If the upstream sends a keep-alive non-2xx response and does not fully drain the body, the desynchronized backend socket is returned to a shared pool. An unauthenticated attacker can exploit this by making a different client read their smuggled response, which can lead to information disclosure, potentially exposing authenticated or private content from other requests. The ForwardAuth middleware can also be affected, further exposing the authentication client pool to desynchronization.
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Description OSIDB Bzimport 2026-08-06 22:30:39 UTC 
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.