CVE-2026-39858 (GCVE-0-2026-39858)

Vulnerability from cvelistv5 – Published: 2026-04-30 20:26 – Updated: 2026-06-30 12:09
VLAI
Title
Traefik: Forwarded alias spoofing top pre-auth decision bypass
Summary
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.
Severity
7.8 (High)
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
8.2 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-290 - Authentication Bypass by Spoofing
  • CWE-306 - Missing Authentication for Critical Function
  • CWE-289 - Authentication Bypass by Alternate Name
Assigner
References
Impacted products
Vendor Product Version
traefik traefik Affected: < 2.11.43
Affected: >= 3.0.0-beta1, < 3.6.14
Affected: >= 3.7.0-ea.1, < 3.7.0-rc.2
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Red Hat Red Hat OpenShift Dev Spaces 3.28     cpe:/a:redhat:openshift_devspaces:3.28::el9
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      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-39858\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-05-04T16:57:57.062955Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-05-04T16:58:09.098Z\"}}], \"cna\": {\"title\": \"Traefik: Forwarded alias spoofing top pre-auth decision bypass\", \"source\": {\"advisory\": \"GHSA-5m6w-wvh7-57vm\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 7.8, \"attackVector\": \"NETWORK\", \"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\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"NONE\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"HIGH\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"HIGH\", \"vulnConfidentialityImpact\": \"NONE\"}}], \"affected\": [{\"vendor\": \"traefik\", \"product\": \"traefik\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003c 2.11.43\"}, {\"status\": \"affected\", \"version\": \"\u003e= 3.0.0-beta1, \u003c 3.6.14\"}, {\"status\": \"affected\", \"version\": \"\u003e= 3.7.0-ea.1, \u003c 3.7.0-rc.2\"}]}], \"references\": [{\"url\": \"https://github.com/traefik/traefik/security/advisories/GHSA-5m6w-wvh7-57vm\", \"name\": \"https://github.com/traefik/traefik/security/advisories/GHSA-5m6w-wvh7-57vm\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/traefik/traefik/releases/tag/v2.11.43\", \"name\": \"https://github.com/traefik/traefik/releases/tag/v2.11.43\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/traefik/traefik/releases/tag/v3.6.14\", \"name\": \"https://github.com/traefik/traefik/releases/tag/v3.6.14\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2\", \"name\": \"https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2\", \"tags\": [\"x_refsource_MISC\"]}], \"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\u0027s ForwardAuth and snippet-based authentication middleware. Traefik\u0027s 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 \\u2014 such as a trusted scheme or host \\u2014 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.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-290\", \"description\": \"CWE-290: Authentication Bypass by Spoofing\"}]}, {\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-306\", \"description\": \"CWE-306: Missing Authentication for Critical Function\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-04-30T20:26:26.300Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-39858\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-05-04T16:58:14.458Z\", \"dateReserved\": \"2026-04-07T19:13:20.379Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-04-30T20:26:26.300Z\", \"assignerShortName\": \"GitHub_M\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.