CVE-2026-28498

Estado: ModificadaAlta (8.2)—

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm.

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This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9.

CVSS

Versión: 4.0
Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/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
Puntuación base: 8.2

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.26%
Percentil entre todas las CVEs puntuadas: 16
Fecha de la puntuación: 5/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access75 %
Impacto principalT1078 Valid Accountsstealth · persistence · privilege escalation · initial access80 %
Impacto secundarioT1556 Modify Authentication Processdefense impairment · persistence · credential access70 %

Vulnerabilidad en validación de tokens OIDC accesible remotamente sin autenticación previa (AV:N/PR:N). Permite bypass de autenticación (T1078) y manipulación de mecanismos de identidad (T1556) mediante tokens forjados con algoritmos no reconocidos.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Privileged Account Management User Account Management Password Policies Multi-factor Authentication Application Developer Guidance Active Directory Configuration

Tecnologías afectadas (1)

Authlib — Authlib

CWE

CWE-354, CWE-573
CWE-325

Referencias

JSON original (NVD)

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      "value": "Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9."
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      "lang": "es",
      "value": "Authlib es una biblioteca Python que construye servidores OAuth y OpenID Connect. Antes de la versión 1.6.9, se identificó una vulnerabilidad a nivel de biblioteca en la biblioteca Python Authlib con respecto a la validación de los tokens de ID de OpenID Connect (OIDC). Específicamente, la lógica interna de verificación de hash (_verify_hash) responsable de validar las reclamaciones at_hash (Hash de Token de Acceso) y c_hash (Hash de Código de Autorización) exhibe un comportamiento fail-open al encontrar un algoritmo criptográfico no compatible o desconocido. Esta falla permite a un atacante eludir las protecciones de integridad obligatorias al suministrar un token de ID falsificado con un parámetro de encabezado alg deliberadamente no reconocido. La biblioteca intercepta el estado no compatible y devuelve silenciosamente True (validación aprobada), violando inherentemente los principios fundamentales de diseño criptográfico y las especificaciones directas de OIDC. Este problema ha sido parcheado en la versión 1.6.9."
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  "lastModified": "2026-09-10T13:18:01.797",
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