FKIE_CVE-2026-71254
Vulnerability from fkie_nvd - Published: 2026-08-05 12:18 - Updated: 2026-08-05 13:24
Severity
Summary
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.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"product": "nanoMODBUS",
"programFiles": [
"nanomodbus.c"
],
"vendor": "debevv",
"versions": [
{
"lessThanOrEqual": "1.23.0",
"status": "affected",
"version": "0",
"versionType": "semver"
}
]
}
],
"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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\u0027s 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",
"lastModified": "2026-08-05T13:24:49.680",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 5.9,
"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-71254",
"options": [
{
"exploitation": "none"
},
{
"automatable": "yes"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-05T12:29:36.579901Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-08-05T12:18:57.600",
"references": [
{
"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
"url": "https://github.com/debevv/nanoMODBUS"
},
{
"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
"url": "https://github.com/debevv/nanoMODBUS/blob/master/nanomodbus.c"
}
],
"sourceIdentifier": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
"vulnStatus": "Received",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-787"
}
],
"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
"type": "Secondary"
}
]
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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