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CVE-2026-42923

Estado: AnalizadaMedia (6.9)—

NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound.

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Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.

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).

Tecnologías afectadas (1)

Nlnetlabs — Unbound

CWE

Referencias

JSON original (NVD)

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  "id": "CVE-2026-42923",
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          "role": "CISA Coordinator",
          "options": [
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              "exploitation": "none"
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              "technicalImpact": "partial"
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          "version": "2.0.3",
          "timestamp": "2026-05-20T12:10:04.210764Z"
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          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
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          "attackComplexity": "LOW",
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          "privilegesRequired": "NONE",
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          "Automatable": "NOT_DEFINED",
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          "baseSeverity": "MEDIUM",
          "valueDensity": "NOT_DEFINED",
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          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
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  "published": "2026-05-20T10:16:27.630",
  "references": [
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      "tags": [
        "Mitigation",
        "Vendor Advisory"
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  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
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      "description": [
        {
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          "value": "CWE-407"
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  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations."
    },
    {
      "lang": "es",
      "value": "NLnet Labs Unbound hasta la versión 1.25.0 inclusive tiene una vulnerabilidad en el validador DNSSEC donde la ruta de código para consultar la caché negativa de registros DS no tiene en cuenta el límite de cálculos de hash NSEC3 introducido en la versión 1.19.1. Esto conduce a una degradación del servicio durante el ataque. Un adversario que controla una zona firmada con DNSSEC puede explotar esto firmando registros NSEC3 con iteraciones aceptablemente altas para delegaciones secundarias y consultando un Unbound vulnerable. Unbound seguirá realizando los cálculos de hash permitidos en los registros NSEC3 y no limitará el trabajo mediante la mitigación introducida en la versión 1.19.1. Como efecto secundario, se mantendrá un bloqueo global para la caché negativa durante la duración del hashing, bloqueando otros hilos que necesitan consultar la caché negativa. Ataques coordinados podrían elevar la vulnerabilidad a denegación de servicio. Unbound 1.25.1 contiene un parche con una corrección para limitar la ruta de código vulnerable con el límite existente para los cálculos de hash NSEC3."
    }
  ],
  "lastModified": "2026-07-24T10:10:00.197",
  "configurations": [
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