Bug 2531524 (CVE-2026-88011)

Summary: CVE-2026-88011 github.com/traefik/traefik: Traefik: Identity spoofing via dot-form header alias
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: urgent    
Version: unspecifiedCC: sdawley
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Traefik, an open-source HTTP reverse proxy and load balancer. A remote attacker can exploit this vulnerability by sending a specially crafted dot-form header, such as X.Authenticated.User. Due to a discrepancy in how Go and certain backend systems (like CGI, WSGI, PHP, and NGINX) interpret these headers, the backend may consume the client's supplied value instead of the identity asserted by Traefik. This allows for identity spoofing for any header managed by Traefik, potentially leading to unauthorized access or actions.
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Description OSIDB Bzimport 2026-09-10 15:42:26 UTC 
Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.