FKIE_CVE-2026-42959

Vulnerability from fkie_nvd - Published: 2026-05-20 10:16 - Updated: 2026-07-24 10:10
Severity
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
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.
References
sep@nlnetlabs.nlhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42959.txtMitigation, Vendor Advisory
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:19752
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:23231
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:24365
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/errata/RHSA-2026:24369
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/security/cve/CVE-2026-42959
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://bugzilla.redhat.com/show_bug.cgi?id=2479806
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42959.json
Impacted products
Vendor Product Version
nlnetlabs unbound *
To clipboard 

{
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          "product": "Unbound",
          "vendor": "NLnet Labs",
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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."
    },
    {
      "lang": "es",
      "value": "NLnet Labs Unbound hasta e incluyendo la versi\u00f3n 1.25.0 tiene una vulnerabilidad de denegaci\u00f3n 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 validaci\u00f3n, el c\u00f3digo usa el contador incorrecto para calcular los offsets de escritura para los rrsets de la secci\u00f3n ADDITIONAL. La duplicaci\u00f3n de DNAME podr\u00eda aumentar el recuento de la secci\u00f3n ANSWER y el filtrado de autoridad podr\u00eda disminuir el recuento de la secci\u00f3n 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 soluci\u00f3n para usar los contadores adecuados para calcular los offsets de escritura."
    }
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  "lastModified": "2026-07-24T10:10:00.197",
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          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
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          "valueDensity": "NOT_DEFINED",
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.