Vulnerability-Lookup

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

Vulnerability from cvelistv5 – Published: 2026-09-10 15:31 – Updated: 2026-09-15 14:42

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

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-15 14:42 UTC

CWE

CWE-290 - Authentication Bypass by Spoofing

Assigner

GitHub_M mitre root Scorecard

References

5 references

URL	Tags
https://github.com/traefik/traefik/security/advis…	x_refsource_CONFIRM
https://github.com/traefik/traefik/pull/13720	x_refsource_MISC
https://github.com/traefik/traefik/commit/0331801…	x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v…	x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v3.7.12	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
traefik	traefik	Affected: < 2.11.56 Affected: >= 3.0.0, < 3.7.12	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-88011",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-15T14:42:09.176083Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-15T14:42:22.088Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "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",
              "lang": "en",
              "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": "2026-09-15T14:42:22.088Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-88011",
      "date": "2026-09-30",
      "epss": "0.0042",
      "percentile": "0.33913"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "traefik",
                "vendor": "traefik",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 2.11.56"
                  },
                  {
                    "status": "affected",
                    "version": "\u003e= 3.0.0, \u003c 3.7.12"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
                  {
                    "criteria": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "CF2BF7E5-86D5-4141-AD3F-3189F996CCC8",
                    "versionEndExcluding": "2.11.56",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "DA63A7E8-A5BB-4456-965E-F493CCC6D3C5",
                    "versionEndExcluding": "3.7.12",
                    "versionStartIncluding": "3.0.0",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "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."
          }
        ],
        "id": "CVE-2026-88011",
        "lastModified": "2026-09-15T15:17:24.163",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 2.8,
              "impactScore": 5.2,
              "source": "nvd@nist.gov",
              "type": "Primary"
            }
          ],
          "cvssMetricV40": [
            {
              "cvssData": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "availabilityRequirement": "NOT_DEFINED",
                "baseScore": 5.3,
                "baseSeverity": "MEDIUM",
                "confidentialityRequirement": "NOT_DEFINED",
                "exploitMaturity": "NOT_DEFINED",
                "integrityRequirement": "NOT_DEFINED",
                "modifiedAttackComplexity": "NOT_DEFINED",
                "modifiedAttackRequirements": "NOT_DEFINED",
                "modifiedAttackVector": "NOT_DEFINED",
                "modifiedPrivilegesRequired": "NOT_DEFINED",
                "modifiedSubAvailabilityImpact": "NOT_DEFINED",
                "modifiedSubConfidentialityImpact": "NOT_DEFINED",
                "modifiedSubIntegrityImpact": "NOT_DEFINED",
                "modifiedUserInteraction": "NOT_DEFINED",
                "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
                "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
                "modifiedVulnIntegrityImpact": "NOT_DEFINED",
                "privilegesRequired": "LOW",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "HIGH",
                "subIntegrityImpact": "HIGH",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "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",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "NONE",
                "vulnIntegrityImpact": "NONE",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-88011",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-15T14:42:09.176083Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-09-10T16:18:07.933",
        "references": [
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Patch"
            ],
            "url": "https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8"
          },
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Issue Tracking",
              "Patch"
            ],
            "url": "https://github.com/traefik/traefik/pull/13720"
          },
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Release Notes"
            ],
            "url": "https://github.com/traefik/traefik/releases/tag/v2.11.56"
          },
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Release Notes"
            ],
            "url": "https://github.com/traefik/traefik/releases/tag/v3.7.12"
          },
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Patch",
              "Vendor Advisory"
            ],
            "url": "https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-290"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Critical",
      "current_release_date": "2026-09-22T16:43:44+00:00",
      "cve": "CVE-2026-88011",
      "id": "CVE-2026-88011",
      "initial_release_date": "2026-09-10T15:31:55.215000+00:00",
      "product_status:known_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "github.com/traefik/traefik: Traefik: Identity spoofing via dot-form header alias",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-88011.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-88011",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "total"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-09-15T14:42:09.176083Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-09-15T14:42:15.765Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "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",
                  "lang": "en",
                  "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": "2026-09-15T14:42:22.088Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-88011

Vulnerability from fkie_nvd - Published: 2026-09-10 16:18 - Updated: 2026-09-15 15:17

Severity

8.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8	Patch
security-advisories@github.com	https://github.com/traefik/traefik/pull/13720	Issue Tracking, Patch
security-advisories@github.com	https://github.com/traefik/traefik/releases/tag/v2.11.56	Release Notes
security-advisories@github.com	https://github.com/traefik/traefik/releases/tag/v3.7.12	Release Notes
security-advisories@github.com	https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c	Patch, Vendor Advisory

Impacted products

	Vendor	Product	Version
	traefik	traefik	*
	traefik	traefik	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "traefik",
          "vendor": "traefik",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.11.56"
            },
            {
              "status": "affected",
              "version": "\u003e= 3.0.0, \u003c 3.7.12"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "CF2BF7E5-86D5-4141-AD3F-3189F996CCC8",
              "versionEndExcluding": "2.11.56",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "DA63A7E8-A5BB-4456-965E-F493CCC6D3C5",
              "versionEndExcluding": "3.7.12",
              "versionStartIncluding": "3.0.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "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."
    }
  ],
  "id": "CVE-2026-88011",
  "lastModified": "2026-09-15T15:17:24.163",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 8.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 5.2,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "LOW",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "HIGH",
          "subIntegrityImpact": "HIGH",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "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",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-88011",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-09-15T14:42:09.176083Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-09-10T16:18:07.933",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Issue Tracking",
        "Patch"
      ],
      "url": "https://github.com/traefik/traefik/pull/13720"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Release Notes"
      ],
      "url": "https://github.com/traefik/traefik/releases/tag/v2.11.56"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Release Notes"
      ],
      "url": "https://github.com/traefik/traefik/releases/tag/v3.7.12"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ],
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-290"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-RF44-J88R-HH8C

Vulnerability from github – Published: 2026-09-10 20:28 – Updated: 2026-09-10 20:28

Summary

Traefik: ForwardAuth identity spoofing via dot-form header alias

Details

Summary

There is a medium severity vulnerability in Traefik's handling of request headers whose name aliases another header name. Go canonicalizes header names on dashes only, so X-Auth-User, X_Auth_User and X.Auth.User are three distinct headers to Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX, and others) collapse all of them into the same variable. A client can therefore smuggle an alias of a header that Traefik manages past the middleware managing it — for example a dot-form X.Authenticated.User alongside the canonical X-Authenticated-User written by the ForwardAuth middleware — and have such a backend read the client-supplied value instead of the identity Traefik asserted. Any header Traefik sets is exposed, not only ForwardAuth's. This is an incomplete-fix sibling of GHSA-x677-9fxg-v5c5, which blocked only the underscore form.

The mitigation is the new aliasHeadersStrategy entry point option. It defaults to keep, which preserves the previous behavior for backwards compatibility, so it must be explicitly set to delete or reject to take effect.

Traefik v1.x, the v2 releases up to v2.11.55 and the v3 releases from v3.0.0 to v3.7.11 are affected. The unmaintained lines among them will not receive a patch of their own, and the remedy for their users is to upgrade to v2.11.56 or v3.7.12 and set aliasHeadersStrategy.

Patches

https://github.com/traefik/traefik/releases/tag/v2.11.56
https://github.com/traefik/traefik/releases/tag/v3.7.12

For more information

If you have any questions or comments about this advisory, please open an issue.

Original Description ### Summary Traefik's ForwardAuth middleware removes the configured canonical identity header before copying the value returned by the auth service. However, a client-supplied dot-form alias such as `X.Authenticated.User` survives both this replacement and `underscoreHeadersStrategy: delete`. The tested PHP 8.2 built-in SAPI maps `X-Authenticated-User` and `X.Authenticated.User` to the same `HTTP_X_AUTHENTICATED_USER` server variable. In Traefik's tested HTTP/1 backend path, the client value is serialized last and overrides the identity asserted by ForwardAuth. A client whom ForwardAuth permits as a lower-privilege identity can therefore be treated by the backend as another user or role. ### Details At `v3.7.10`, `pkg/server/server_entrypoint_tcp.go:800-818` removes or rejects only names containing `_`. After successful authentication, `pkg/middlewares/auth/forward.go:314-326` deletes and replaces only the canonical `authResponseHeaders` key. The dot alias remains in `req.Header` and the standard reverse proxy forwards both legal field names. Go's HTTP/1 writer sorts header names lexically, placing `X-Authenticated-User` before `X.Authenticated.User`. PHP then collapses both into one `$_SERVER` key, so the attacker value deterministically wins. This is an incomplete-fix sibling of `GHSA-x677-9fxg-v5c5`: the published underscore input is blocked by the new entry-point strategy, while the dot input bypasses that mitigation on the current stable release. ### PoC [traefik-dot-forwardauth-poc.zip](https://github.com/user-attachments/files/30898195/traefik-dot-forwardauth-poc.zip) run:

docker compose up -d
bash verify.sh
docker compose down

The decisive request is:

GET /probe HTTP/1.1
Host: 127.0.0.1:18080
X.Authenticated.User: admin
Connection: close

Expected backend identity: `lab-user`, as returned by ForwardAuth. Observed on `v3.7.10`: `admin`. The script also verifies that requests without the alias, with the canonical header, and with the already-fixed underscore alias all produce `lab-user`. ### Impact Applications that authorize requests using a ForwardAuth-provided identity header can receive an attacker-selected username or role instead. This was runtime-verified with PHP 8.2.27 and 8.2.33; impact on other normalization-prone backends is conditional. A lower-privilege permitted client may consequently impersonate another user or administrative role, affecting confidentiality and integrity. This report does not claim bypass of a ForwardAuth denial: the auth service must first permit the request.

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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.11.56"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.7.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-88011"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-290"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-10T20:28:15Z",
    "nvd_published_at": "2026-09-10T16:18:07Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nThere is a medium severity vulnerability in Traefik\u0027s handling of request headers whose name aliases another header name. Go canonicalizes header names on dashes only, so `X-Auth-User`, `X_Auth_User` and `X.Auth.User` are three distinct headers to Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX, and others) collapse all of them into the same variable. A client can therefore smuggle an alias of a header that Traefik manages past the middleware managing it \u2014 for example a dot-form `X.Authenticated.User` alongside the canonical `X-Authenticated-User` written by the ForwardAuth middleware \u2014 and have such a backend read the client-supplied value instead of the identity Traefik asserted. Any header Traefik sets is exposed, not only ForwardAuth\u0027s. This is an incomplete-fix sibling of GHSA-x677-9fxg-v5c5, which blocked only the underscore form.\n\nThe mitigation is the new `aliasHeadersStrategy` entry point option. It defaults to `keep`, which preserves the previous behavior for backwards compatibility, so it must be explicitly set to `delete` or `reject` to take effect.\n\nTraefik v1.x, the v2 releases up to v2.11.55 and the v3 releases from v3.0.0 to v3.7.11 are affected. The unmaintained lines among them will not receive a patch of their own, and the remedy for their users is to upgrade to v2.11.56 or v3.7.12 and set `aliasHeadersStrategy`.\n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v2.11.56\n- https://github.com/traefik/traefik/releases/tag/v3.7.12\n\n## For more information\n\nIf you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal Description\u003c/summary\u003e\n\n### Summary\nTraefik\u0027s ForwardAuth middleware removes the configured canonical identity header before copying the value returned by the auth service. However, a client-supplied dot-form alias such as `X.Authenticated.User` survives both this replacement and `underscoreHeadersStrategy: delete`.\n\nThe tested PHP 8.2 built-in SAPI maps `X-Authenticated-User` and `X.Authenticated.User` to the same `HTTP_X_AUTHENTICATED_USER` server variable. In Traefik\u0027s tested HTTP/1 backend path, the client value is serialized last and overrides the identity asserted by ForwardAuth.\n\nA client whom ForwardAuth permits as a lower-privilege identity can therefore be treated by the backend as another user or role.\n\n### Details\nAt `v3.7.10`, `pkg/server/server_entrypoint_tcp.go:800-818` removes or rejects only names containing `_`. After successful authentication, `pkg/middlewares/auth/forward.go:314-326` deletes and replaces only the canonical `authResponseHeaders` key. The dot alias remains in `req.Header` and the standard reverse proxy forwards both legal field names.\n\nGo\u0027s HTTP/1 writer sorts header names lexically, placing `X-Authenticated-User` before `X.Authenticated.User`. PHP then collapses both into one `$_SERVER` key, so the attacker value deterministically wins.\n\nThis is an incomplete-fix sibling of `GHSA-x677-9fxg-v5c5`: the published underscore input is blocked by the new entry-point strategy, while the dot input bypasses that mitigation on the current stable release.\n\n### PoC\n[traefik-dot-forwardauth-poc.zip](https://github.com/user-attachments/files/30898195/traefik-dot-forwardauth-poc.zip)\n\nrun:\n```bash\ndocker compose up -d\nbash verify.sh\ndocker compose down\n```\n\nThe decisive request is:\n\n```http\nGET /probe HTTP/1.1\nHost: 127.0.0.1:18080\nX.Authenticated.User: admin\nConnection: close\n```\n\nExpected backend identity: `lab-user`, as returned by ForwardAuth.\n\nObserved on `v3.7.10`: `admin`.\n\nThe script also verifies that requests without the alias, with the canonical header, and with the already-fixed underscore alias all produce `lab-user`.\n\n### Impact\nApplications that authorize requests using a ForwardAuth-provided identity header can receive an attacker-selected username or role instead. This was runtime-verified with PHP 8.2.27 and 8.2.33; impact on other normalization-prone backends is conditional. A lower-privilege permitted client may consequently impersonate another user or administrative role, affecting confidentiality and integrity.\n\nThis report does not claim bypass of a ForwardAuth denial: the auth service must first permit the request.\n\n\n\u003c/details\u003e\n---",
  "id": "GHSA-rf44-j88r-hh8c",
  "modified": "2026-09-10T20:28:15Z",
  "published": "2026-09-10T20:28:15Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-88011"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/pull/13720"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/traefik/traefik"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v2.11.56"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.7.12"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Traefik: ForwardAuth identity spoofing via dot-form header alias"
}

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

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

FKIE_CVE-2026-88011

GHSA-RF44-J88R-HH8C

Summary

Patches

For more information

Tags

Sightings

Nomenclature

Related by attack behaviour