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CVE-2026-42959

Estado: ModificadaAlta (8.7)—

NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot.

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Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.

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 de red sin autenticación (AV:N/PR:N/UI:N) con impacto de disponibilidad (VA:H). Unbound expuesto como servicio DNS remotamente explotable. DNSSEC validator crash causado por respuestas maliciosas agota disponibilidad del servicio.

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)

Nlnetlabs — Unbound

CWE

Referencias

JSON original (NVD)

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      "value": "NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets."
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      "value": "NLnet Labs Unbound hasta e incluyendo la versión 1.25.0 tiene una vulnerabilidad de denegación de servicio en el validador DNSSEC que puede llevar a un fallo dadas respuestas maliciosas de upstream. Cuando Unbound construye mensajes de respuesta de seguimiento para la validación, el código usa el contador incorrecto para calcular los offsets de escritura para los rrsets de la sección ADDITIONAL. La duplicación de DNAME podría aumentar el recuento de la sección ANSWER y el filtrado de autoridad podría disminuir el recuento de la sección AUTHORITY y crear una ranura de array no inicializada. Combinando estos dos, el validador luego desreferencia este puntero no inicializado, causando un fallo inmediato del proceso. Un adversario que controla un dominio firmado con DNSSEC puede activar este error con una sola consulta configurando una cadena DNAME con CNAMEs no firmados y una respuesta que contenga registros AUTHORITY no firmados junto con registros glue ADDITIONAL firmados. Unbound 1.25.1 contiene un parche con una solución para usar los contadores adecuados para calcular los offsets de escritura."
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