CVE-2026-55973

{
  "id": "CVE-2026-55973",
  "sourceIdentifier": "[email protected]",
  "published": "2026-07-22T14:17:21.663",
  "lastModified": "2026-10-24T13:10:00.147",
  "vulnStatus": "Analyzed",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon."
    },
    {
      "lang": "es",
      "value": "En NLnet Labs Unbound 1.23.0 hasta la versión 1.25.1 inclusive, cuando se configura ’dns-error-reporting: yes’, se lee la opción EDNS Report-Channel (código 18) de la última respuesta ascendente y se utiliza la longitud de la opción como la longitud del dominio del agente. Cuando se realiza una verificación de nombre de dominio en el dominio del agente, la longitud devuelta no se utiliza y si el dominio del agente es seguido por datos basura, esos bytes se mueven a la cola del nombre de consulta de informe sintético ’_er.’. Ese nombre de consulta se utiliza posteriormente en el iterador a través de una subconsulta para enviar el Informe de Error de DNS y cuando Unbound intenta recorrer ese nombre de consulta durante ’find_closest_of_type()’, elimina etiquetas utilizando la longitud del nombre de consulta en lugar de detenerse en la raíz incrustada, avanza un byte más allá de ella, y alimenta el primer byte de datos basura a ’dname_query_hash()’ como una longitud de etiqueta, sobrescribiendo la variable de pila ’labuf’. Una respuesta ascendente ordinaria de una zona delegada que el atacante controla es suficiente para terminar el demonio."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "NLnet Labs",
          "product": "Unbound",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "1.23.0",
              "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:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-07-22T14:05:39.964116Z",
          "id": "CVE-2026-55973",
          "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-20"
        }
      ]
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "operator": "OR",
          "negate": false,
          "cpeMatch": [
            {
              "vulnerable": true,
              "criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*",
              "versionStartIncluding": "1.23.0",
              "versionEndExcluding": "1.25.2",
              "matchCriteriaId": "A2A7D63D-3E41-493D-A64C-F20C3FFABDBD"
            }
          ]
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55973.txt",
      "source": "[email protected]",
      "tags": [
        "Vendor Advisory"
      ]
    }
  ]
}