CVE-2026-56444

{
  "id": "CVE-2026-56444",
  "sourceIdentifier": "[email protected]",
  "published": "2026-07-22T14:17:22.203",
  "lastModified": "2026-10-24T13:10:00.147",
  "vulnStatus": "Undergoing Analysis",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the serve expired logic drops an aged client reply without performing the correct accounting for the number of reply addresses for the query. Other identical branches outside of serve expired perform the correct decrement. Since the counter is never decremented in such scenario, it can reach the maximum limit and new clients for duplicate in-flight queries are silently dropped resulting in degradation of resolution service. A malicious actor can exploit the vulnerability by querying the resolver for a client-controlled slow-on-demand authoritative zone that can drive the counter past the threshold. Shipped defaults for 'serve-expired-client-timeout: 1800' and 'discard-timeout: 1900' make the branch unreachable."
    },
    {
      "lang": "es",
      "value": "En NLnet Labs Unbound 1.20.0 hasta la versión 1.25.1 inclusive, cuando Unbound está configurado con ’serve-expired: yes’ y ’serve-expired-client-timeout > discard-timeout > 0’ (contrariamente a los valores sugeridos), la rama de ’discard-timeout’ durante la lógica de ’serve expired’ descarta una respuesta de cliente antigua sin realizar la contabilidad correcta para el número de direcciones de respuesta para la consulta. Otras ramas idénticas fuera de ’serve expired’ realizan el decremento correcto. Dado que el contador nunca se decrementa en tal escenario, puede alcanzar el límite máximo y los nuevos clientes para consultas duplicadas en curso se descartan silenciosamente, lo que resulta en una degradación del servicio de resolución. Un actor malicioso puede explotar la vulnerabilidad consultando el resolvedor para una zona autoritativa de respuesta lenta bajo demanda controlada por el cliente que puede llevar el contador más allá del umbral. Los valores predeterminados de fábrica para ’serve-expired-client-timeout: 1800’ y ’discard-timeout: 1900’ hacen que la rama sea inalcanzable."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "NLnet Labs",
          "product": "Unbound",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "1.20.0",
              "lessThan": "1.25.2",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "attackVector": "NETWORK",
          "attackComplexity": "HIGH",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-07-22T13:58:06.496467Z",
          "id": "CVE-2026-56444",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-772"
        }
      ]
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "operator": "OR",
          "negate": false,
          "cpeMatch": [
            {
              "vulnerable": true,
              "criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
              "versionStartIncluding": "1.20.0",
              "versionEndExcluding": "1.25.2",
              "matchCriteriaId": "5DA7F611-366A-4A5F-B687-5DE36841726C"
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  "references": [
    {
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-56444.txt",
      "source": "[email protected]",
      "tags": [
        "Vendor Advisory"
      ]
    }
  ]
}