{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "last_affected": "1.23.0"
              },
              {
                "fixed": "v1.23.0"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "DESCRIPTION"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "91d6782930ee263bc760f27b0cbc5b82773c5f0d"
            }
          ],
          "repo": "https://github.com/debevv/nanomodbus",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "TuranSec",
    "cwe_ids": [
      "CWE-787"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71254.json"
  },
  "details": "nanoMODBUS through v1.23.0 contains an out-of-bounds write in the Modbus server-side handle_read_file_record() function (FC 0x14, Read File Record) in nanomodbus.c. The function validates that the total request size does not exceed 245 bytes and that each sub-request's record_length is at most 124, but it never validates the CUMULATIVE response size across all sub-requests before processing them. The accumulator response_data_size is declared as uint8_t and is incremented by 2 + record_length*2 for each of up to 35 sub-requests; with 35 sub-requests of record_length=124, the cumulative demand is 8750 bytes, which overflows the uint8_t accumulator. A subsequent loop then calls get_n(), an internal function with no bounds checking, once per sub-request to obtain a pointer into the 260-byte msg.buf receive buffer and advances the internal buf_idx by up to 248 bytes per call; swap_regs() then writes to that pointer unconditionally. A single crafted FC 0x14 request from an unauthenticated network client can cause up to ~8490 bytes to be written out of bounds past the 260-byte buffer, corrupting adjacent memory in the server process and leading to denial of service or potential remote code execution, particularly on embedded/bare-metal targets without memory protection.",
  "id": "CVE-2026-71254",
  "modified": "2026-08-07T11:31:20.106093095Z",
  "published": "2026-08-05T11:44:20.214Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/debevv/nanoMODBUS/blob/master/nanomodbus.c"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71254.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-71254"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/debevv/nanoMODBUS"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record()"
}