{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-39858","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","state":"PUBLISHED","assignerShortName":"GitHub_M","dateReserved":"2026-04-07T19:13:20.379Z","datePublished":"2026-04-30T20:26:26.300Z","dateUpdated":"2026-04-30T20:26:26.300Z"},"containers":{"cna":{"title":"Traefik: Forwarded alias spoofing top pre-auth decision bypass","problemTypes":[{"descriptions":[{"cweId":"CWE-290","lang":"en","description":"CWE-290: Authentication Bypass by Spoofing","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-306","lang":"en","description":"CWE-306: Missing Authentication for Critical Function","type":"CWE"}]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"HIGH","subIntegrityImpact":"HIGH","subAvailabilityImpact":"NONE","baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N","version":"4.0"}}],"references":[{"name":"https://github.com/traefik/traefik/security/advisories/GHSA-5m6w-wvh7-57vm","tags":["x_refsource_CONFIRM"],"url":"https://github.com/traefik/traefik/security/advisories/GHSA-5m6w-wvh7-57vm"},{"name":"https://github.com/traefik/traefik/releases/tag/v2.11.43","tags":["x_refsource_MISC"],"url":"https://github.com/traefik/traefik/releases/tag/v2.11.43"},{"name":"https://github.com/traefik/traefik/releases/tag/v3.6.14","tags":["x_refsource_MISC"],"url":"https://github.com/traefik/traefik/releases/tag/v3.6.14"},{"name":"https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2","tags":["x_refsource_MISC"],"url":"https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2"}],"affected":[{"vendor":"traefik","product":"traefik","versions":[{"version":"< 2.11.43","status":"affected"},{"version":">= 3.0.0-beta1, < 3.6.14","status":"affected"},{"version":">= 3.7.0-ea.1, < 3.7.0-rc.2","status":"affected"}]}],"providerMetadata":{"orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M","dateUpdated":"2026-04-30T20:26:26.300Z"},"descriptions":[{"lang":"en","value":"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. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2."}],"source":{"advisory":"GHSA-5m6w-wvh7-57vm","discovery":"UNKNOWN"}}}}