{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-71263", "assignerOrgId": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "state": "PUBLISHED", "assignerShortName": "TuranSec", "dateReserved": "2026-08-05T12:23:34.966Z", "datePublished": "2026-08-05T12:26:11.423Z", "dateUpdated": "2026-08-05T12:52:30.063Z"}, "containers": {"cna": {"title": "FreeModbus LINUXTCP Port Off-by-One Global Buffer Overflow in xMBPortTCPPool()", "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 `if (usTCPFrameBytesLeft > MB_TCP_BUF_SIZE)` uses a strict greater-than comparison instead of greater-than-or-equal against the 263-byte MB_TCP_BUF_SIZE limit. An MBAP frame with a Length field of 264 makes usTCPFrameBytesLeft equal to 263, which passes the flawed check, and the subsequent recv() call writes up to 263 bytes starting at buffer offset 7 into the 263-byte static buffer aucTCPBuf, overflowing it by 7 bytes into the adjacent static variable usTCPBufPos. A single crafted, unauthenticated Modbus TCP packet triggers the overflow, since Modbus has no built-in authentication."}], "problemTypes": [{"descriptions": [{"lang": "en", "description": "CWE-787", "cweId": "CWE-787", "type": "CWE"}]}], "affected": [{"vendor": "cwalter-at", "product": "FreeModbus", "programFiles": ["demo/LINUXTCP/port/porttcp.c"], "versions": [{"version": "0", "lessThanOrEqual": "*", "status": "affected", "versionType": "custom"}], "defaultStatus": "unaffected"}], "metrics": [{"cvssV3_1": {"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"}}], "references": [{"url": "https://github.com/cwalter-at/freemodbus"}, {"url": "https://github.com/cwalter-at/freemodbus/blob/master/demo/LINUXTCP/port/porttcp.c"}], "credits": [{"lang": "en", "value": "Alibek Baxtiyorov", "type": "finder"}], "providerMetadata": {"orgId": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "shortName": "TuranSec", "dateUpdated": "2026-08-05T12:52:30.063Z"}}}}

{}

{}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[0,*]"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "FreeModbus", "source": "cna", "vendor": "cwalter-at"}, "product": "freemodbus", "vendor": "cwalter-at"}], "created": "2026-08-05T14:45:16.597091+00:00", "updated": "2026-08-05T15:30:17.153557+00:00", "vendors": ["cwalter-at", "cwalter-at$PRODUCT$freemodbus"]}