CVE-2025-40556

Persistent controller outage via malformed MSTP message

Published May 13, 2025 · Updated May 13, 2025

Improper input validation in Siemens BACnet ATEC 550-440, 550-441, 550-445, and 550-446 allows attackers to halt devices via MSTP messages. The BACnet MS/TP message handler improperly processes specific crafted messages and leaves the controller in a persistent denial-of-service state. Access to the same BACnet network is required, and normal operation does not resume until the targeted device is power-cycled.

CVSS severity7.1
High
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Siemens BACnet ATEC 550-440, 550-441, 550-445, and 550-446 allows attackers to halt devices via MSTP messages. The BACnet MS/TP message handler improperly processes specific crafted messages and leaves the controller in a persistent denial-of-service state. Access to the same BACnet network is required, and normal operation does not resume until the targeted device is power-cycled.

The record

CVE
CVE-2025-40556
Published
May 13, 2025
Updated
May 13, 2025
Vendor
Siemens
Product
BACnet ATEC 550-441
Classifications
CWE-20, T0814
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2025CVE publishedPublication date reported by the CVE source.
  2. May 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <*

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Siemens · BACnet ATEC 550-441version=0 <*
Siemens · BACnet ATEC 550-446version=0 <*
Siemens · BACnet ATEC 550-445version=0 <*
Siemens · BACnet ATEC 550-440version=0 <*

Published CVSS scores

7.1Siemens AGCVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
6.5Siemens AGCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T0814Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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