{
  "affected": [
    {
      "affectedData": [
        {
          "product": "quicly",
          "vendor": "h2o",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 8b178e6"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:h2o:quicly:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "FD025CC7-B866-4C0E-873A-86908DC9E6BD",
              "versionEndExcluding": "2026-05-29",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, Quicly is vulnerable to a Denial of Service attack through connection state corruption. In QUIC Invariants, the maximum length of a Connection ID is 255 bytes, while QUIC version 1 further restricts the maximum to 20 bytes. Quicly implements QUIC version 1 and therefore its CID buffers are limited to 20 bytes. However, to be able to respond to unknown versions of QUIC, its packet decoder accepts Connection IDs of up to 255 bytes. As its CID buffers are merely 20 bytes long, Quicly must reject QUIC version 1 packets with Connection IDs longer than that. The command line tool bundled with Quicly has had that check, however the library itself lacked such enforcement. As a consequence, when used by applications that lack their own enforcement, the connection state becoming inconsistent to buffer overrun. Fortunately, the overflow stops within the allocated chunk of memory, but nevertheless, the bug leads to assertion failures. This issue has been fixed by commit 8b178e6."
    },
    {
      "lang": "es",
      "value": "Quicly es una implementaci\u00f3n del protocolo QUIC de la IETF destinada principalmente para su uso dentro del servidor HTTP H2O. Antes del commit 8b178e6, Quicly es vulnerable a un ataque de denegaci\u00f3n de servicio a trav\u00e9s de la corrupci\u00f3n del estado de la conexi\u00f3n. En QUIC Invariants, la longitud m\u00e1xima de un ID de Conexi\u00f3n es de 255 bytes, mientras que la versi\u00f3n 1 de QUIC restringe a\u00fan m\u00e1s el m\u00e1ximo a 20 bytes. Quicly implementa la versi\u00f3n 1 de QUIC y, por lo tanto, sus b\u00faferes CID est\u00e1n limitados a 20 bytes. Sin embargo, para poder responder a versiones desconocidas de QUIC, su decodificador de paquetes acepta IDs de Conexi\u00f3n de hasta 255 bytes. Como sus b\u00faferes CID tienen solo 20 bytes de longitud, Quicly debe rechazar los paquetes de la versi\u00f3n 1 de QUIC con IDs de Conexi\u00f3n m\u00e1s largos que eso. La herramienta de l\u00ednea de comandos incluida con Quicly ten\u00eda esa verificaci\u00f3n, sin embargo, la biblioteca misma carec\u00eda de tal aplicaci\u00f3n. Como consecuencia, cuando es utilizado por aplicaciones que carecen de su propia aplicaci\u00f3n, el estado de la conexi\u00f3n se vuelve inconsistente debido a un desbordamiento de b\u00fafer. Afortunadamente, el desbordamiento se detiene dentro del fragmento de memoria asignado, pero, sin embargo, el error conduce a fallos de aserci\u00f3n. Este problema ha sido solucionado por el commit 8b178e6."
    }
  ],
  "id": "CVE-2026-44436",
  "lastModified": "2026-10-24T20:10:00.137",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-44436",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-07-17T10:48:23.373806Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-07-16T23:16:17.143",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/h2o/quicly/commit/8b178e692c51a3b1031612ef89f03a53aac63c15"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://github.com/h2o/quicly/security/advisories/GHSA-v55w-59qx-2v78"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-120"
        },
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}