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CVE-2026-88011 (GCVE-0-2026-88011)

Vulnerability from cvelistv5 – Published: 2026-09-10 15:31 – Updated: 2026-09-10 15:31
VLAI
Title
Traefik: ForwardAuth identity spoofing via dot-form header alias
Summary
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.
Severity
5.3 (Medium)
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
CWE
  • CWE-290 - Authentication Bypass by Spoofing
Assigner
References
Impacted products
Vendor Product Version CPE status
traefik traefik Affected: < 2.11.56
Affected: >= 3.0.0, < 3.7.12
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "traefik",
          "vendor": "traefik",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.11.56"
            },
            {
              "status": "affected",
              "version": "\u003e= 3.0.0, \u003c 3.7.12"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "LOW",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "HIGH",
            "subIntegrityImpact": "HIGH",
            "userInteraction": "NONE",
            "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-290",
              "description": "CWE-290: Authentication Bypass by Spoofing",
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              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-10T15:31:55.215Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c"
        },
        {
          "name": "https://github.com/traefik/traefik/pull/13720",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/traefik/traefik/pull/13720"
        },
        {
          "name": "https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8"
        },
        {
          "name": "https://github.com/traefik/traefik/releases/tag/v2.11.56",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/traefik/traefik/releases/tag/v2.11.56"
        },
        {
          "name": "https://github.com/traefik/traefik/releases/tag/v3.7.12",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/traefik/traefik/releases/tag/v3.7.12"
        }
      ],
      "source": {
        "advisory": "GHSA-rf44-j88r-hh8c",
        "discovery": "UNKNOWN"
      },
      "title": "Traefik: ForwardAuth identity spoofing via dot-form header alias"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-88011",
    "datePublished": "2026-09-10T15:31:55.215Z",
    "dateReserved": "2026-09-09T19:19:27.407Z",
    "dateUpdated": "2026-09-10T15:31:55.215Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-88011",
      "date": "2026-09-13",
      "epss": "0.00246",
      "percentile": "0.15944"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-88011\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-09-10T16:18:07.933\",\"lastModified\":\"2026-09-10T19:54:25.810\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"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.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"traefik\",\"product\":\"traefik\",\"versions\":[{\"version\":\"\u003c 2.11.56\",\"status\":\"affected\"},{\"version\":\"\u003e= 3.0.0, \u003c 3.7.12\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV40\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X\",\"baseScore\":5.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"attackRequirements\":\"PRESENT\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"vulnConfidentialityImpact\":\"NONE\",\"vulnIntegrityImpact\":\"NONE\",\"vulnAvailabilityImpact\":\"NONE\",\"subConfidentialityImpact\":\"HIGH\",\"subIntegrityImpact\":\"HIGH\",\"subAvailabilityImpact\":\"NONE\",\"exploitMaturity\":\"NOT_DEFINED\",\"confidentialityRequirement\":\"NOT_DEFINED\",\"integrityRequirement\":\"NOT_DEFINED\",\"availabilityRequirement\":\"NOT_DEFINED\",\"modifiedAttackVector\":\"NOT_DEFINED\",\"modifiedAttackComplexity\":\"NOT_DEFINED\",\"modifiedAttackRequirements\":\"NOT_DEFINED\",\"modifiedPrivilegesRequired\":\"NOT_DEFINED\",\"modifiedUserInteraction\":\"NOT_DEFINED\",\"modifiedVulnConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedVulnIntegrityImpact\":\"NOT_DEFINED\",\"modifiedVulnAvailabilityImpact\":\"NOT_DEFINED\",\"modifiedSubConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedSubIntegrityImpact\":\"NOT_DEFINED\",\"modifiedSubAvailabilityImpact\":\"NOT_DEFINED\",\"Safety\":\"NOT_DEFINED\",\"Automatable\":\"NOT_DEFINED\",\"Recovery\":\"NOT_DEFINED\",\"valueDensity\":\"NOT_DEFINED\",\"vulnerabilityResponseEffort\":\"NOT_DEFINED\",\"providerUrgency\":\"NOT_DEFINED\"}}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-290\"}]}],\"references\":[{\"url\":\"https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/traefik/traefik/pull/13720\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/traefik/traefik/releases/tag/v2.11.56\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/traefik/traefik/releases/tag/v3.7.12\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c\",\"source\":\"security-advisories@github.com\"}]}}"
  }
}



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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.

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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.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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