CVE-2025-40556
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 · uneditedA vulnerability has been identified in BACnet ATEC 550-440 (All versions), BACnet ATEC 550-441 (All versions), BACnet ATEC 550-445 (All versions), BACnet ATEC 550-446 (All versions). Affected devices improperly handle specific incoming BACnet MSTP messages. This could allow an attacker residing in the same BACnet network to send a specially crafted MSTP message that results in a denial of service condition of the targeted device. A power cycle is required to restore the device's normal operation.
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 · moderate confidenceThe BACnet ATEC 550 series devices (440, 441, 445, 446) have a vulnerability in their BACnet MSTP message processing. An attacker with network adjacency to the BACnet segment can send specially crafted MSTP frames that cause the device to enter a denial of service state, requiring a power cycle to recover.
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
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 device modelQuery the device via BACnet WhoIs service or check physical device labeling to confirm the exact model number is one of: ATEC 550, ATEC 440, ATEC 441, ATEC 445, or ATEC 446.Affected if The device model is any of the ATEC 550 series variants (440, 441, 445, 446).
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Verify BACnet protocol is enabledSend a BACnet WhoIs request to the device broadcast address (typically 255.255.255.255) on BACnet port 47808 (0xBAC0) and confirm the device responds with its Device ID and network capabilities.Affected if BACnet protocol stack is active and the device responds to BACnet queries.
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Confirm MSTP transport in useInspect the device BACnet configuration or capture network traffic to verify the transport layer is using MSTP (Master-Slave/Token-Passing) rather than IP (BACnet/IP). MSTP operates over serial RS-485 or similar fieldbus, not over IP.Affected if The device is configured to use BACnet MSTP as its transport protocol.
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Assess network adjacency exposureDetermine if the BACnet MSTP segment is accessible to untrusted network segments. Check if the device is on an isolated VLAN or if MSTP frames could be injected from adjacent network paths.Affected if The BACnet MSTP segment is reachable from network segments that contain untrusted or unauthorized devices.
If the device is an ATEC 550 series model (440, 441, 445, or 446), has BACnet MSTP enabled, and the BACnet segment is network-adjacent to untrusted systems, the environment is affected by this CVE.
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 dataIsolate BACnet network segments and implement strict access controls to prevent unauthorized MSTP traffic. Monitor for anomalous BACnet traffic and coordinate with the vendor for firmware updates.
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-40556 — 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-2025-40556 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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