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CVE-2026-9076

Estado: AnalizadaAlta (7.5)—

Issue summary: When CMS password-based decryption (RFC 3211 / PWRI key unwrap) processes attacker-supplied CMS data, an attacker-chosen stream-mode KEK cipher can trigger a heap out-of-bounds read in kek_unwrap_key().

Impact summary: A heap buffer over-read may trigger a crash which leads to Denial of Service for an application if the input buffer ends at a memory page boundary and the following page is unmapped. There is no information disclosure as the over-read bytes are not revealed to the attacker.

The key unwrapping function performs a check-byte test as specified in the RFC that reads 7 bytes from a heap allocation that is based on the wrapped key length from the message.

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There is a minimum length check based on the block length of the wrapping cipher. However the cipher is selected from an OID carried in the attacker's PWRI keyEncryptionAlgorithm with no requirement that the cipher be a block cipher. When an attacker selects a stream-mode cipher the guard will be ineffective and the allocated buffer containing the unwrapped key can be too small to fit the check-bytes specified in the RFC and a buffer over-read can happen.

Applications calling CMS_decrypt() or CMS_decrypt_set1_password() (equivalently openssl cms -decrypt -pwri_password ...) on untrusted CMS data are vulnerable to this issue. No password knowledge is required: the over-read happens during the unwrap attempt before any authentication succeeds.

The over-read is limited to a few bytes and is not written to output, so there is no information disclosure. Triggering a crash requires the allocation to border unmapped memory, which is unlikely with the normal allocator.

The FIPS modules are not affected by this issue.

CVSS

Probabilidad de explotación (EPSS)

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.

Vulnerabilidad en OpenSSL accesible remotamente sin autenticación (AV:N/PR:N/UI:N). El atacante envía datos CMS maliciosos que causan lectura fuera de límites en la memoria, provocando DoS por crash cuando el buffer bordea memoria no mapeada.

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

Filter Network TrafficVulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkApplication Isolation and Sandboxing

Tecnologías afectadas (1)

Openssl — Openssl

CWE

Referencias

JSON original (NVD)

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      "value": "Issue summary: When CMS password-based decryption (RFC 3211 / PWRI key unwrap)\nprocesses attacker-supplied CMS data, an attacker-chosen stream-mode KEK\ncipher can trigger a heap out-of-bounds read in kek_unwrap_key().\n\nImpact summary: A heap buffer over-read may trigger a crash which leads to\nDenial of Service for an application if the input buffer ends at a memory\npage boundary and the following page is unmapped. There is no information\ndisclosure as the over-read bytes are not revealed to the attacker.\n\nThe key unwrapping function performs a check-byte test as specified in the\nRFC that reads 7 bytes from a heap allocation that is based on the wrapped\nkey length from the message. There is a minimum length check based on the\nblock length of the wrapping cipher. However the cipher is selected from\nan OID carried in the attacker's PWRI keyEncryptionAlgorithm with no\nrequirement that the cipher be a block cipher. When an attacker selects\na stream-mode cipher the guard will be ineffective and the allocated buffer\ncontaining the unwrapped key can be too small to fit the check-bytes\nspecified in the RFC and a buffer over-read can happen.\n\nApplications calling CMS_decrypt() or CMS_decrypt_set1_password()\n(equivalently openssl cms -decrypt -pwri_password ...) on untrusted CMS\ndata are vulnerable to this issue. No password knowledge is required: the\nover-read happens during the unwrap attempt before any authentication\nsucceeds.\n\nThe over-read is limited to a few bytes and is not written to output, so\nthere is no information disclosure. Triggering a crash requires the\nallocation to border unmapped memory, which is unlikely with the normal\nallocator.\n\nThe FIPS modules are not affected by this issue."
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      "value": "Resumen del problema: Cuando el descifrado basado en contraseña de CMS (RFC 3211 / desenvolvimiento de clave PWRI) procesa datos CMS suministrados por el atacante, un cifrado KEK en modo de flujo elegido por el atacante puede desencadenar una lectura fuera de límites en el heap en kek_unwrap_key().\n\nResumen del impacto: Una lectura excesiva del búfer del heap puede desencadenar un fallo que lleva a la denegación de servicio para una aplicación si el búfer de entrada termina en un límite de página de memoria y la página siguiente no está mapeada. No hay revelación de información ya que los bytes leídos en exceso no se revelan al atacante.\n\nLa función de desenvolvimiento de clave realiza una prueba de bytes de verificación según lo especificado en el RFC que lee 7 bytes de una asignación en el heap que se basa en la longitud de la clave envuelta del mensaje. Hay una verificación de longitud mínima basada en la longitud de bloque del cifrado de envoltura. Sin embargo, el cifrado se selecciona de un OID transportado en el algoritmo de cifrado de clave PWRI del atacante sin el requisito de que el cifrado sea un cifrado de bloque. Cuando un atacante selecciona un cifrado en modo de flujo, la protección será ineficaz y el búfer asignado que contiene la clave desenvuelta puede ser demasiado pequeño para contener los bytes de verificación especificados en el RFC y puede ocurrir una lectura excesiva del búfer.\n\nLas aplicaciones que llaman a 'CMS_decrypt()' o 'CMS_decrypt_set1_password()' (equivalentemente OpenSSL cms -decrypt -pwri_password ...) en datos CMS no confiables son vulnerables a este problema. No se requiere conocimiento de la contraseña: la lectura excesiva ocurre durante el intento de desenvolvimiento antes de que cualquier autenticación tenga éxito.\n\nLa lectura excesiva está limitada a unos pocos bytes y no se escribe en la salida, por lo que no hay revelación de información. Desencadenar un fallo requiere que la asignación limite con memoria no mapeada, lo cual es poco probable con el asignador normal.\n\nLos módulos FIPS no se ven afectados por este problema."
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