{"id":"CVE-2026-71254","aliases":["EUVD-2026-53331","GHSA-29rm-wvww-5gjv"],"status":"published","title":"nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record()","description":"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.","severity":{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00553,"percentile":0.4666,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-787"],"published":"2026-08-05T11:44:20Z","modified":"2026-10-28T02:30:38Z","products":[{"vendor":"debevv","product":"nanomodbus"}],"references":[{"url":"https://github.com/debevv/nanoMODBUS","tags":["third-party-advisory","advisory"]},{"url":"https://github.com/debevv/nanoMODBUS/blob/master/nanomodbus.c","tags":["third-party-advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-71254","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-29rm-wvww-5gjv"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71254.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-71254","title":"nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record()","description":"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.","status":"published","published":"2026-08-05T11:44:20.214Z","modified":"2026-08-10T11:46:13.975Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"cna"}],"cwes":["CWE-787"],"updated_at":"2026-11-02T14:19:49.199185Z"}],"euvd":[{"id":"EUVD-2026-53331","description":"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.","status":"published","published":"2026-08-05T11:44:20Z","modified":"2026-08-10T11:46:13Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"updated_at":"2026-11-02T18:02:05.732685Z"}],"ghsa":[{"id":"GHSA-29rm-wvww-5gjv","title":"nanoMODBUS through v1.23.0 contains an out-of-bounds write in the Modbus server-side...","description":"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.","status":"published","published":"2026-08-05T12:31:33Z","modified":"2026-08-05T12:31:34Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"cwes":["CWE-787"],"updated_at":"2026-11-02T15:10:06.632203Z"}],"nvd":[{"id":"CVE-2026-71254","description":"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.","status":"published","published":"2026-08-05T12:18:57.6Z","modified":"2026-10-24T15:10:00.19Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical","assessor":"secondary"}],"cwes":["CWE-787"],"updated_at":"2026-11-02T14:12:35.031043Z"}],"osv":[{"id":"CVE-2026-71254","title":"nanoMODBUS Server-Side Out-of-Bounds Write in handle_read_file_record()","description":"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.","status":"published","published":"2026-08-05T11:44:20.214Z","modified":"2026-10-28T02:30:38.466684367Z","cvss":[{"version":"3.1","score":9.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"critical"}],"cwes":["CWE-787"],"updated_at":"2026-11-02T15:45:15.164658Z"}]}}