CVE-2026-71263

{
  "id": "CVE-2026-71263",
  "sourceIdentifier": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
  "published": "2026-08-05T13:24:50.473",
  "lastModified": "2026-10-24T15:10:00.190",
  "vulnStatus": "Deferred",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "The LINUXTCP port of FreeModbus contains an off-by-one bounds check in xMBPortTCPPool (demo/LINUXTCP/port/porttcp.c). The check uses a strict greater-than comparison instead of greater-than-or-equal against the 263-byte MB_TCP_BUF_SIZE limit."
    },
    {
      "lang": "es",
      "value": "El puerto LINUXTCP de FreeModbus contiene una comprobación de límites ’off-by-one’ en xMBPortTCPPool() (demo/LINUXTCP/port/porttcp.c). La comprobación ’if (usTCPFrameBytesLeft mayor que MB_TCP_BUF_SIZE)’ utiliza una comparación estrictamente mayor que en lugar de mayor o igual que contra el límite de 263 bytes de MB_TCP_BUF_SIZE. Un frame MBAP con un campo Length de 264 hace que usTCPFrameBytesLeft sea igual a 263, lo que pasa la comprobación defectuosa, y la subsiguiente llamada a recv() escribe hasta 263 bytes comenzando en el desplazamiento 7 del búfer en el búfer estático de 263 bytes aucTCPBuf, desbordándolo en 7 bytes en la variable estática adyacente usTCPBufPos. Un único paquete Modbus TCP manipulado y no autenticado desencadena el desbordamiento, ya que Modbus no tiene autenticación incorporada."
    }
  ],
  "affected": [
    {
      "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
      "affectedData": [
        {
          "vendor": "cwalter-at",
          "product": "FreeModbus",
          "defaultStatus": "unaffected",
          "programFiles": [
            "demo/LINUXTCP/port/porttcp.c"
          ],
          "versions": [
            {
              "version": "0",
              "lessThanOrEqual": "*",
              "versionType": "custom",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 5.2
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-08-05T15:39:27.280961Z",
          "id": "CVE-2026-71263",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/cwalter-at/freemodbus",
      "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c"
    },
    {
      "url": "https://github.com/cwalter-at/freemodbus/blob/master/demo/LINUXTCP/port/porttcp.c",
      "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c"
    }
  ]
}