Siemens BACnet ATEC Devices
As of January 10, 2023, CISA will no longer be updating ICS security advisories for Siemens product vulnerabilities beyond the initial advisory. For the most up-to-date information on vulnerabilities in this advisory, please see Siemens' ProductCERT Security Advisories (CERT Services | Services | Siemens Global).
1. EXECUTIVE SUMMARY
- CVSS v4 7.1
- ATTENTION: Exploitable from adjacent network/low attack complexity
- Vendor: Siemens
- Equipment: BACnet ATEC Devices
- Vulnerability: Improper Input Validation
2. RISK EVALUATION
Successful exploitation of this vulnerability 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.
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
Siemens reports the following BACnet ATEC products are affected:
- Siemens BACnet ATEC 550-440: All versions
- Siemens BACnet ATEC 550-441: All versions
- Siemens BACnet ATEC 550-445: All versions
- Siemens BACnet ATEC 550-446: All versions
3.2 VULNERABILITY OVERVIEW
3.2.1 IMPROPER INPUT VALIDATION CWE-20
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.
CVE-2025-40556 has been assigned to this vulnerability. A CVSS v3.1 base score of 6.5 has been calculated; the CVSS vector string is (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
A CVSS v4 score has also been calculated for CVE-2025-40556. A base score of 7.1 has been calculated; the CVSS vector string is (CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N).
3.3 BACKGROUND
- CRITICAL INFRASTRUCTURE SECTORS: Commercial Facilities
- COUNTRIES/AREAS DEPLOYED: Worldwide
- COMPANY HEADQUARTERS LOCATION: Germany
3.4 RESEARCHER
Qiguang Zhang, Zhen Ling, Junzhou Luo, and Chongqing Lei from Southeast University, Xinwen Fu and Christopher Morales from University of Massachusetts Lowell, and Yue Zhang from Drexel University reported this vulnerability to Siemens.
4. MITIGATIONS
Currently, Siemens has no plan to fix this vulnerability.
As a general security measure, Siemens recommends protecting network access to devices with appropriate mechanisms. To operate the devices in a protected IT environment, Siemens recommends configuring the environment according to Siemens' operational guidelines for industrial security and following recommendations in the product manuals.
Additional information on industrial security by Siemens can be found on the Siemens industrial security webpage
For more information see the associated Siemens security advisory SSA-828116 in HTML and CSAF.
CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.
CISA also provides a section for control systems security recommended practices on the ICS webpage on cisa.gov. Several CISA products detailing cyber defense best practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.
CISA encourages organizations to implement recommended cybersecurity strategies for proactive defense of ICS assets.
Additional mitigation guidance and recommended practices are publicly available on the ICS webpage at cisa.gov in the technical information paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.
Organizations observing suspected malicious activity should follow established internal procedures and report findings to CISA for tracking and correlation against other incidents.
No known public exploitation specifically targeting this vulnerability has been reported to CISA at this time.
5. UPDATE HISTORY
- May 15, 2025: Initial Republication of Siemens SSA-828116
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Vendor
- Siemens