{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-88879","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","state":"PUBLISHED","assignerShortName":"VulnCheck","dateReserved":"2026-09-10T11:24:26.196Z","datePublished":"2026-09-10T13:05:30.872Z","dateUpdated":"2026-09-10T15:04:00.316Z"},"containers":{"cna":{"providerMetadata":{"orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","shortName":"VulnCheck","dateUpdated":"2026-09-10T13:05:30.872Z"},"datePublic":"2026-08-27T00:00:00.000Z","title":"Traefik before v2.11.56 Identity Spoofing via Header Alias","descriptions":[{"lang":"en","value":"Traefik is an HTTP reverse proxy and load balancer. In Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11, header names are canonicalized only on dashes, so X-Auth-User, X_Auth_User and X.Auth.User are treated as three distinct headers by Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX and others) collapse them into a single variable. A client can therefore smuggle a dot-form alias of a header that Traefik manages past the middleware managing it — for example supplying X.Authenticated.User alongside the canonical X-Authenticated-User written by the ForwardAuth middleware — causing such a backend to read the client-supplied value instead of the identity Traefik asserted. In the tested configuration (PHP 8.2 built-in SAPI over an HTTP/1 backend path), Go's lexical header ordering makes the attacker-supplied value win deterministically, so a client that ForwardAuth admits as a low-privilege identity can be treated by the backend as a different user or role. Any header Traefik sets is affected, not only ForwardAuth's. This is an incomplete fix for GHSA-x677-9fxg-v5c5, which blocked only the underscore form. Fixed in v2.11.56 and v3.7.12, which add the aliasHeadersStrategy entry-point option; because it defaults to 'keep' for backwards compatibility, it must be explicitly set to 'delete' or 'reject' for the fix to take effect. Unmaintained release lines will not receive a patch."}],"problemTypes":[{"descriptions":[{"lang":"en","description":"Authentication Bypass by Spoofing","cweId":"CWE-290","type":"CWE"}]}],"affected":[{"vendor":"traefik","product":"traefik","defaultStatus":"unaffected","packageURL":"pkg:golang/Traefik","versions":[{"version":"0","status":"affected","versionType":"semver","lessThan":"2.11.56"},{"version":"2.11.56","status":"unaffected","versionType":"semver"}]},{"vendor":"traefik","product":"traefik","defaultStatus":"unaffected","packageURL":"pkg:golang/Traefik","versions":[{"version":"3.0.0","status":"affected","versionType":"semver","lessThanOrEqual":"3.7.13"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*","versionEndExcluding":"2.11.56"}]}]},{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*","versionStartIncluding":"3.0.0","versionEndIncluding":"3.7.13"}]}]}],"metrics":[{"format":"CVSS","cvssV4_0":{"version":"4.0","vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"LOW","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"HIGH","subIntegrityImpact":"HIGH","subAvailabilityImpact":"NONE","baseScore":5.3,"baseSeverity":"MEDIUM"}}],"references":[{"url":"https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c","tags":["vendor-advisory"],"name":"GitHub Security Advisory (GHSA-rf44-j88r-hh8c)"},{"name":"VulnCheck Advisory: Traefik before v2.11.56 Identity Spoofing via Header Alias","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/traefik-before-2.11.56-identity-spoofing-via-header-alias"}],"credits":[{"lang":"en","value":"velgusgus599","type":"reporter"}],"x_generator":{"engine":"vulncheck-endgame"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-10T15:03:25.506535Z","id":"CVE-2026-88879","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-09-10T15:04:00.316Z"}}]}}