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CVE-2026-7383

Estado: AnalizadaAlta (8.1)—

Issue summary: A signed integer overflow when sizing the destination buffer for Unicode output in ASN1_mbstring_ncopy() can lead to a heap buffer overflow.

Impact summary: A heap buffer overflow may lead to a crash or possibly attacker controlled code execution or other undefined behaviour.

In ASN1_mbstring_copy() and ASN1_mbstring_ncopy() the destination size for Unicode output is computed in a signed int: by left shift of the input character count for BMPSTRING (UTF-16) and UNIVERSALSTRING (UTF-32), and by summing per-character byte counts for UTF8STRING.

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The calculation overflows when the input reaches around 2^30 characters. In the worst case (UNIVERSALSTRING at 2^30 characters) the size wraps to zero, OPENSSL_malloc(1) is called, and the subsequent character copy writes several gigabytes past the one-byte allocation.

X.509 certificate processing routes through ASN1_STRING_set_by_NID(), whose DIRSTRING_TYPE mask excludes UNIVERSALSTRING and whose per-NID size limits cap the input length; no network protocol or certificate-handling path in OpenSSL exercises the overflow. Triggering the bug requires an application that calls ASN1_mbstring_copy() or ASN1_mbstring_ncopy() directly, or registers a custom string type via ASN1_STRING_TABLE_add(), with attacker-controlled input on the order of half a gigabyte or more. For these reasons this issue was assigned Low severity.

The FIPS modules in 4.0, 3.6, 3.5, 3.4 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

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.

Vector CVSS AV:N/AC:H (red sin privilegios) sugiere T1190. Heap buffer overflow puede resultar en ejecución de código, pero requiere aplicación personalizada con entrada de medio gigabyte (casos raros).

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 ManagementVulnerability ScanningRestrict Web-Based ContentNetwork SegmentationLimit Software InstallationLimit Access to Resource Over Network

Tecnologías afectadas (1)

Openssl — Openssl

CWE

Referencias

JSON original (NVD)

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      "value": "Issue summary: A signed integer overflow when sizing the destination\nbuffer for Unicode output in ASN1_mbstring_ncopy() can lead to a heap\nbuffer overflow.\n\nImpact summary: A heap buffer overflow may lead to a crash or possibly\nattacker controlled code execution or other undefined behaviour.\n\nIn ASN1_mbstring_copy() and ASN1_mbstring_ncopy() the destination\nsize for Unicode output is computed in a signed int: by left shift\nof the input character count for BMPSTRING (UTF-16) and\nUNIVERSALSTRING (UTF-32), and by summing per-character byte counts\nfor UTF8STRING. The calculation overflows when the input reaches\naround 2^30 characters. In the worst case (UNIVERSALSTRING at 2^30\ncharacters) the size wraps to zero, OPENSSL_malloc(1) is called, and\nthe subsequent character copy writes several gigabytes past the\none-byte allocation.\n\nX.509 certificate processing routes through ASN1_STRING_set_by_NID(),\nwhose DIRSTRING_TYPE mask excludes UNIVERSALSTRING and whose per-NID\nsize limits cap the input length; no network protocol or\ncertificate-handling path in OpenSSL exercises the overflow.\nTriggering the bug requires an application that calls\nASN1_mbstring_copy() or ASN1_mbstring_ncopy() directly, or registers\na custom string type via ASN1_STRING_TABLE_add(), with\nattacker-controlled input on the order of half a gigabyte or more.\nFor these reasons this issue was assigned Low severity.\n\nThe FIPS modules in 4.0, 3.6, 3.5, 3.4 and 3.0 are not affected by\nthis issue, as the affected code is outside the OpenSSL FIPS module\nboundary."
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      "value": "Resumen del problema: Un desbordamiento de entero con signo al dimensionar el búfer de destino para la salida Unicode en ASN1_mbstring_ncopy() puede conducir a un desbordamiento de búfer de pila.\n\nResumen del impacto: Un desbordamiento de búfer de pila puede conducir a un fallo o posiblemente a la ejecución de código controlado por el atacante u otro comportamiento indefinido.\n\nEn ASN1_mbstring_copy() y ASN1_mbstring_ncopy() el tamaño de destino para la salida Unicode se calcula en un entero con signo: mediante un desplazamiento a la izquierda del recuento de caracteres de entrada para BMPSTRING (UTF-16) y UNIVERSALSTRING (UTF-32), y sumando los recuentos de bytes por carácter para UTF8STRING. El cálculo desborda cuando la entrada alcanza alrededor de 2^30 caracteres. En el peor de los casos (UNIVERSALSTRING con 2^30 caracteres) el tamaño se ajusta a cero, se llama a OPENSSL_malloc(1), y la copia de caracteres subsiguiente escribe varios gigabytes más allá de la asignación de un byte.\n\nEl procesamiento de certificados X.509 se encamina a través de ASN1_STRING_set_by_NID(), cuya máscara DIRSTRING_TYPE excluye UNIVERSALSTRING y cuyos límites de tamaño por NID restringen la longitud de entrada; ningún protocolo de red o ruta de manejo de certificados en OpenSSL ejerce el desbordamiento. Activar el error requiere una aplicación que llama a ASN1_mbstring_copy() o ASN1_mbstring_ncopy() directamente, o registra un tipo de cadena personalizado a través de ASN1_STRING_TABLE_add(), con entrada controlada por el atacante del orden de medio gigabyte o más. Por estas razones, a este problema se le asignó una severidad Baja.\n\nLos módulos FIPS en 4.0, 3.6, 3.5, 3.4 y 3.0 no se ven afectados por este problema, ya que el código afectado está fuera del límite del módulo FIPS de OpenSSL."
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  "lastModified": "2026-07-23T08:10:00.137",
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