CVE-2026-71263

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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "FreeModbus", "programFiles": ["demo/LINUXTCP/port/porttcp.c"], "vendor": "cwalter-at", "versions": [{"lessThanOrEqual": "*", "status": "affected", "version": "0", "versionType": "custom"}]}], "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c"}], "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 comprobaci\u00f3n de l\u00edmites \u2019off-by-one\u2019 en xMBPortTCPPool() (demo/LINUXTCP/port/porttcp.c). La comprobaci\u00f3n \u2019if (usTCPFrameBytesLeft mayor que MB_TCP_BUF_SIZE)\u2019 utiliza una comparaci\u00f3n estrictamente mayor que en lugar de mayor o igual que contra el l\u00edmite 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 comprobaci\u00f3n defectuosa, y la subsiguiente llamada a recv() escribe hasta 263 bytes comenzando en el desplazamiento 7 del b\u00fafer en el b\u00fafer est\u00e1tico de 263 bytes aucTCPBuf, desbord\u00e1ndolo en 7 bytes en la variable est\u00e1tica adyacente usTCPBufPos. Un \u00fanico paquete Modbus TCP manipulado y no autenticado desencadena el desbordamiento, ya que Modbus no tiene autenticaci\u00f3n incorporada."}], "id": "CVE-2026-71263", "lastModified": "2026-10-24T15:10:00.190", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 9.1, "baseSeverity": "CRITICAL", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 5.2, "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-71263", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-08-05T15:39:27.280961Z", "version": "2.0.3"}}]}, "published": "2026-08-05T13:24:50.473", "references": [{"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "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"}], "sourceIdentifier": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-787"}], "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "type": "Secondary"}]}

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