CVE-2026-29972
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditednanoMODBUS through v1.22.0 has a stack-based buffer overflow in recv_read_registers_res() in nanomodbus.c. When a client calls nmbs_read_holding_registers() or nmbs_read_input_registers(), the library writes register data from the server response to the caller-provided buffer based on the response's byte_count field before validating that byte_count matches the requested quantity. A malicious Modbus TCP server can send a response with byte_count=250 (125 registers) regardless of the requested quantity, causing up to 248 bytes of attacker-controlled data to overflow the buffer, potentially allowing remote code execution.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidencenanoMODBUS through v1.22.0 contains a stack-based buffer overflow in recv_read_registers_res() in nanomodbus.c. When processing responses to nmbs_read_holding_registers() or nmbs_read_input_registers(), the library writes register data from the server's response directly to a caller-provided buffer using the response's byte_count field without first validating that byte_count matches the requested quantity, allowing a malicious Modbus TCP server to send byte_count=250 (125 registers) and overflow the buffer with up to 248 bytes of attacker-controlled data.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify nanoMODBUS library versionLocate the nanomodbus.c source file or the library package in your project. Check the file header for version information, or inspect your dependency manifest (e.g., package.json, CMakeLists.txt, requirements.txt, or git submodule info) for the nanoMODBUS version pinned.Affected if The installed version is 1.22.0 or earlier (any version through v1.22.0).
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Verify use of vulnerable read register functionsSearch your codebase for calls to nmbs_read_holding_registers() or nmbs_read_input_registers() functions. These are the functions that invoke the vulnerable recv_read_registers_res() internally.Affected if Your application calls either nmbs_read_holding_registers() or nmbs_read_input_registers() to communicate with a Modbus server.
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Check if application validates response byte_countInspect the code that handles responses from nmbs_read_holding_registers() or nmbs_read_input_registers(). Look for explicit validation that compares the response byte_count against the expected quantity (requested register count * 2) before the data is used or copied.Affected if No application-layer validation exists that verifies byte_count matches the requested quantity before processing the register data.
You are affected if your project uses nanoMODBUS version 1.22.0 or earlier AND calls nmbs_read_holding_registers() or nmbs_read_input_registers() to communicate with Modbus servers whose integrity you cannot guarantee.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpdate to nanoMODBUS v1.22.1 or later which adds validation of byte_count against the requested quantity before writing to the buffer. Until then, ensure only trusted Modbus servers are contacted, or implement application-layer validation of response byte counts.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-29972 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-29972 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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