{"api_version":"1","generated_at":"2026-05-01T12:32:17+00:00","cve":"CVE-2026-39858","urls":{"html":"https://cve.report/CVE-2026-39858","api":"https://cve.report/api/cve/CVE-2026-39858.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-39858","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-39858"},"summary":{"title":"Traefik: Forwarded alias spoofing top pre-auth decision bypass","description":"Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's ForwardAuth and snippet-based authentication middleware. Traefik's forwarded-header sanitization logic targets only canonical header names (e.g., X-Forwarded-Proto) and does not strip or normalize alias variants that use underscores instead of dashes (e.g., X_Forwarded_Proto). These unsanitized alias headers are forwarded intact to the authentication backend. When the backend normalizes underscore and dash header forms equivalently, an attacker can inject spoofed trust context — such as a trusted scheme or host — through the alias headers and bypass authentication on protected routes without valid credentials. 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