CVE-2026-66883

Full vulnerability record from the local CVENow database.

Description

Improper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (Oidcc.Plug.Authorize module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session. This vulnerability is associated with program files lib/oidcc/plug/authorize.ex and lib/oidcc/plug/authorization_callback.ex, and program routines Oidcc.Plug.Authorize.call/2 and Oidcc.Plug.AuthorizationCallback.call/2. Oidcc.Plug.Authorize.call/2 reads the initiating client's user agent with get_req_header(conn, "User-Agent"). Plug lowercases incoming header names, but get_req_header/2 matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and nil is written into the session. On the callback side, Oidcc.Plug.AuthorizationCallback treats a stored nil user agent as nothing to compare and returns :ok without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with check_useragent: true, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent. The impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled check_useragent are not affected in practice, since they never expected the binding. The corresponding lookup in Oidcc.Plug.AuthorizationCallback correctly uses the lowercase key and is not affected. This issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0.

Severity

MEDIUM

CVSS score

6.3 (v4.0)

Vulnerability status

Awaiting Analysis

Source identifier

6b3ad84c-e1a6-4bf7-a703-f496b71e49db

Published

2026-08-04 12:16:36.163000

Last modified

2026-10-23 23:10:00.157000

View original CVE JSON

{
  "id": "CVE-2026-66883",
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "published": "2026-08-04T12:16:36.163",
  "lastModified": "2026-10-23T23:10:00.157",
  "vulnStatus": "Awaiting Analysis",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Improper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (Oidcc.Plug.Authorize module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session.\n\nThis vulnerability is associated with program files lib/oidcc/plug/authorize.ex and lib/oidcc/plug/authorization_callback.ex, and program routines Oidcc.Plug.Authorize.call/2 and Oidcc.Plug.AuthorizationCallback.call/2.\n\nOidcc.Plug.Authorize.call/2 reads the initiating client's user agent with get_req_header(conn, \"User-Agent\"). Plug lowercases incoming header names, but get_req_header/2 matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and nil is written into the session. On the callback side, Oidcc.Plug.AuthorizationCallback treats a stored nil user agent as nothing to compare and returns :ok without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with check_useragent: true, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent.\n\nThe impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled check_useragent are not affected in practice, since they never expected the binding. The corresponding lookup in Oidcc.Plug.AuthorizationCallback correctly uses the lowercase key and is not affected.\n\nThis issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0."
    },
    {
      "lang": "es",
      "value": "La vulnerabilidad de manejo inadecuado de la distinción entre mayúsculas y minúsculas en Erlang Ecosystem Foundation oidcc_plug (módulo Oidcc.Plug.Authorize) vuelve inerte la vinculación de la sesión del agente de usuario, eliminando un control de defensa en profundidad contra la repetición de una sesión robada.\n\nEsta vulnerabilidad está asociada con los archivos de programa lib/oidcc/plug/authorize.ex y lib/oidcc/plug/authorization_callback.ex, y las rutinas de programa Oidcc.Plug.Authorize.call/2 y Oidcc.Plug.AuthorizationCallback.call/2.\n\nOidcc.Plug.Authorize.call/2 lee el agente de usuario del cliente iniciador con get_req_header(conn, ’User-Agent’). Plug convierte a minúsculas los nombres de encabezado entrantes, pero get_req_header/2 coincide exactamente con la clave proporcionada y no realiza ninguna normalización propia, por lo que la búsqueda con mayúsculas y minúsculas siempre devuelve una lista vacía y nil se escribe en la sesión. En el lado de la devolución de llamada, Oidcc.Plug.AuthorizationCallback trata un agente de usuario nil almacenado como nada que comparar y devuelve :ok sin inspeccionar la solicitud. Los dos comportamientos se combinan de modo que la verificación pasa incondicionalmente en cada solicitud, incluso para implementaciones que optaron explícitamente con check_useragent: true, y una devolución de llamada de autorización puede completarse desde un agente de usuario diferente al que inició el flujo sin detección. La verificación falla abierta silenciosamente, sin error y sin entrada de registro, por lo que una implementación no puede saber que la vinculación está ausente.\n\nEl impacto se limita a la defensa en profundidad. La verificación inerte no permite por sí misma a un atacante completar un flujo de autorización; elimina una capa que de otro modo dificultaría el uso de una sesión robada o filtrada, como una cookie de sesión exfiltrada repetida desde un cliente diferente. Las verificaciones de CSRF/estado, nonce y PKCE no se ven afectadas y continúan funcionando. Las implementaciones que nunca habilitaron check_useragent no se ven afectadas en la práctica, ya que nunca esperaron la vinculación. La búsqueda correspondiente en Oidcc.Plug.AuthorizationCallback utiliza correctamente la clave en minúsculas y no se ve afectada.\n\nEste problema afecta a oidcc_plug: desde 0.1.0-alpha.3 antes de 0.5.0."
    }
  ],
  "affected": [
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "affectedData": [
        {
          "vendor": "Erlang Ecosystem Foundation",
          "product": "oidcc_plug",
          "defaultStatus": "unaffected",
          "collectionURL": "https://repo.hex.pm",
          "packageName": "oidcc_plug",
          "cpes": [
            "cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*"
          ],
          "modules": [
            "Elixir.Oidcc.Plug.Authorize",
            "Elixir.Oidcc.Plug.AuthorizationCallback"
          ],
          "programFiles": [
            "lib/oidcc/plug/authorize.ex",
            "lib/oidcc/plug/authorization_callback.ex"
          ],
          "programRoutines": [
            {
              "name": "'Elixir.Oidcc.Plug.Authorize':call/2"
            },
            {
              "name": "'Elixir.Oidcc.Plug.AuthorizationCallback':call/2"
            }
          ],
          "repo": "https://github.com/erlef/oidcc_plug",
          "packageURL": "pkg:hex/oidcc_plug",
          "versions": [
            {
              "version": "0.1.0-alpha.3",
              "lessThan": "0.5.0",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Erlang Ecosystem Foundation",
          "product": "oidcc_plug",
          "defaultStatus": "unaffected",
          "collectionURL": "https://github.com",
          "packageName": "erlef/oidcc_plug",
          "cpes": [
            "cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*"
          ],
          "modules": [
            "Elixir.Oidcc.Plug.Authorize",
            "Elixir.Oidcc.Plug.AuthorizationCallback"
          ],
          "programFiles": [
            "lib/oidcc/plug/authorize.ex",
            "lib/oidcc/plug/authorization_callback.ex"
          ],
          "programRoutines": [
            {
              "name": "'Elixir.Oidcc.Plug.Authorize':call/2"
            },
            {
              "name": "'Elixir.Oidcc.Plug.AuthorizationCallback':call/2"
            }
          ],
          "repo": "https://github.com/erlef/oidcc_plug",
          "packageURL": "pkg:github/erlef/oidcc_plug",
          "versions": [
            {
              "version": "0a75fb139d8e2686d1b75e0d48962323d2181673",
              "lessThan": "f15e52c5750aaba701104b10ed96cfac063bd557",
              "versionType": "git",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV40": [
      {
        "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "type": "Secondary",
        "cvssData": {
          "version": "4.0",
          "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/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": 6.3,
          "baseSeverity": "MEDIUM",
          "attackVector": "NETWORK",
          "attackComplexity": "HIGH",
          "attackRequirements": "PRESENT",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "LOW",
          "vulnAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "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"
        }
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-08-04T12:27:16.535019Z",
          "id": "CVE-2026-66883",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-178"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://cna.erlef.org/cves/CVE-2026-66883.html",
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
    },
    {
      "url": "https://github.com/erlef/oidcc_plug/commit/f15e52c5750aaba701104b10ed96cfac063bd557",
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
    },
    {
      "url": "https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc",
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
    },
    {
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-66883",
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
    },
    {
      "url": "https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"
    }
  ]
}