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CVE-2026-55735

Full vulnerability record from the local CVENow database.

Description

Improper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to revoke a victim's session with a forged token. Guardian.revoke/3 in lib/guardian.ex decodes the supplied token with peek/1, which performs no signature verification (it only base64-decodes the JWT header and payload). The resulting unverified claims are forwarded directly to the configured token module's revoke callback and the implementation's on_revoke callback, a state-mutating sink. The sibling operations refresh/2 and exchange/4 both call decode_and_verify first, so the signature is checked before anything acts on the claims; revoke/3 is the only state-mutating path that acts on claims without verifying the signature. An attacker who knows or guesses a victim's identifying claim values (jti, sub) can forge a JWT carrying those claims, sign it with an arbitrary key, and submit it to any endpoint that funnels a caller-supplied token into Guardian.revoke/3 (the standard logout / session-revocation pattern). When the token module mutates state keyed by the claims (whitelist deletion or blacklist insertion, for example a GuardianDb-style store), the victim's legitimate session is evicted. This is an unauthenticated session-revocation denial of service; the attacker never needs the signing secret. This issue affects guardian: from 1.0.0 before 2.4.1.

Severity
HIGH
CVSS score
8.2 (v4.0)
Vulnerability status
Analyzed
Source identifier
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Published
2026-08-01 19:16:42.510000
Last modified
2026-10-23 22:10:00.160000
View original CVE JSON 
{
  "id": "CVE-2026-55735",
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "published": "2026-08-01T19:16:42.510",
  "lastModified": "2026-10-23T22:10:00.160",
  "vulnStatus": "Analyzed",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Improper Verification of Cryptographic Signature in ueberauth guardian allows an unauthenticated attacker to revoke a victim's session with a forged token.\n\nGuardian.revoke/3 in lib/guardian.ex decodes the supplied token with peek/1, which performs no signature verification (it only base64-decodes the JWT header and payload). The resulting unverified claims are forwarded directly to the configured token module's revoke callback and the implementation's on_revoke callback, a state-mutating sink. The sibling operations refresh/2 and exchange/4 both call decode_and_verify first, so the signature is checked before anything acts on the claims; revoke/3 is the only state-mutating path that acts on claims without verifying the signature.\n\nAn attacker who knows or guesses a victim's identifying claim values (jti, sub) can forge a JWT carrying those claims, sign it with an arbitrary key, and submit it to any endpoint that funnels a caller-supplied token into Guardian.revoke/3 (the standard logout / session-revocation pattern). When the token module mutates state keyed by the claims (whitelist deletion or blacklist insertion, for example a GuardianDb-style store), the victim's legitimate session is evicted. This is an unauthenticated session-revocation denial of service; the attacker never needs the signing secret.\n\nThis issue affects guardian: from 1.0.0 before 2.4.1."
    },
    {
      "lang": "es",
      "value": "Verificación Incorrecta de Firma Criptográfica en ueberauth guardian permite a un atacante no autenticado revocar la sesión de una víctima con un token falsificado.\n\nGuardian.revoke/3 en lib/guardian.ex decodifica el token suministrado con peek/1, que no realiza verificación de firma (solo decodifica en base64 el encabezado y la carga útil del JWT). Las reclamaciones no verificadas resultantes se reenvían directamente a la devolución de llamada ’revoke’ del módulo de token configurado y a la devolución de llamada ’on_revoke’ de la implementación, un sumidero que muta el estado. Las operaciones hermanas refresh/2 y exchange/4 ambas llaman primero a decode_and_verify, por lo que la firma se verifica antes de que cualquier cosa actúe sobre las reclamaciones; revoke/3 es la única ruta que muta el estado y que actúa sobre las reclamaciones sin verificar la firma.\n\nUn atacante que conoce o adivina los valores de reclamación identificativos de una víctima (jti, sub) puede falsificar un JWT que contenga esas reclamaciones, firmarlo con una clave arbitraria y enviarlo a cualquier punto final que canalice un token suministrado por el llamador a Guardian.revoke/3 (el patrón estándar de cierre de sesión / revocación de sesión). Cuando el módulo de token muta el estado indexado por las reclamaciones (eliminación de lista blanca o inserción en lista negra, por ejemplo, un almacén estilo GuardianDb), la sesión legítima de la víctima es expulsada. Esto es una denegación de servicio de revocación de sesión no autenticada; el atacante nunca necesita el secreto de firma.\n\nEste problema afecta a guardian: desde 1.0.0 antes de 2.4.1."
    }
  ],
  "affected": [
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "affectedData": [
        {
          "vendor": "ueberauth",
          "product": "guardian",
          "defaultStatus": "unaffected",
          "collectionURL": "https://repo.hex.pm",
          "packageName": "guardian",
          "cpes": [
            "cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"
          ],
          "modules": [
            "'Elixir.Guardian'"
          ],
          "programFiles": [
            "lib/guardian.ex"
          ],
          "programRoutines": [
            {
              "name": "'Elixir.Guardian':revoke/3"
            }
          ],
          "repo": "https://github.com/ueberauth/guardian",
          "packageURL": "pkg:hex/guardian",
          "versions": [
            {
              "version": "1.0.0",
              "lessThan": "2.4.1",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "ueberauth",
          "product": "guardian",
          "defaultStatus": "unaffected",
          "collectionURL": "https://github.com",
          "packageName": "ueberauth/guardian",
          "cpes": [
            "cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*"
          ],
          "modules": [
            "'Elixir.Guardian'"
          ],
          "programFiles": [
            "lib/guardian.ex"
          ],
          "programRoutines": [
            {
              "name": "'Elixir.Guardian':revoke/3"
            }
          ],
          "repo": "https://github.com/ueberauth/guardian",
          "packageURL": "pkg:github/ueberauth/guardian",
          "versions": [
            {
              "version": "d65227145f72b290106c06cecbe42728fbf05fe2",
              "lessThan": "2bd7a8c29770d423d855c0a4965caa6c3e486901",
              "versionType": "git",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
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          "baseScore": 8.2,
          "baseSeverity": "HIGH",
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          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnAvailabilityImpact": "HIGH",
          "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"
        }
      }
    ],
    "cvssMetricV31": [
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        "source": "[email protected]",
        "type": "Primary",
        "cvssData": {
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          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
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      }
    ],
    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
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          "id": "CVE-2026-55735",
          "options": [
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              "exploitation": "poc"
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          "role": "CISA Coordinator",
          "version": "2.0.3"
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  "weaknesses": [
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      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-347"
        }
      ]
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "operator": "OR",
          "negate": false,
          "cpeMatch": [
            {
              "vulnerable": true,
              "criteria": "cpe:2.3:a:ueberauth:guardian:*:*:*:*:*:*:*:*",
              "versionStartIncluding": "1.0.0",
              "versionEndExcluding": "2.4.1",
              "matchCriteriaId": "D61141EA-5786-4D7B-8780-55707F97E793"
            }
          ]
        }
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    }
  ],
  "references": [
    {
      "url": "https://cna.erlef.org/cves/CVE-2026-55735.html",
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
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}