ICS Advisory (ICSA-21-194-12)

Siemens VxWorks-based Industrial Products

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  • CVSS v3 9.8
  • ATTENTION: Exploitable remotely/low attack complexity
  • Vendor: Siemens
  • Equipment: Wind River VxWorks-based Industrial Products
  • Vulnerability: Heap-based Buffer Overflow


Successful exploitation of this vulnerability could allow an attacker to cause a heap-based buffer overflow.



Siemens reports this vulnerability affects the following Wind River VxWorks-based industrial products:

  • RUGGEDCOM WIN Subscriber Station: All versions
  • SCALANCE X200-4 P IRT: All versions
  • SCALANCE X201-3P IRT: All versions
  • SCALANCE X201-3P IRT PRO: All versions
  • SCALANCE X202-2 IRT: All versions
  • SCALANCE X202-2P IRT: All versions
  • SCALANCE X202-2P IRT PRO: All versions
  • SCALANCE X204 IRT: All versions
  • SCALANCE X204 IRT PRO: All versions
  • SCALANCE X204-2 (incl. SIPLUS NET variant): All versions
  • SCALANCE X204-2FM: All versions
  • SCALANCE X204-2LD (incl. SIPLUS NET variant): All versions
  • SCALANCE X204-2LD TS: All versions
  • SCALANCE X204-2TS: All versions
  • SCALANCE X206-1: All versions
  • SCALANCE X206-1LD: All versions
  • SCALANCE X208: All versions
  • SCALANCE X208 PRO: All versions
  • SCALANCE X212-2: All versions
  • SCALANCE X212-2LD: All versions
  • SCALANCE X216: All versions
  • SCALANCE X224: All versions
  • SCALANCE X300/X408 family (incl. SIPLUS NET variants): All versions
  • SCALANCE XF201-3P IRT: All versions
  • SCALANCE XF202-2P IRT: All versions
  • SCALANCE XF204: All versions
  • SCALANCE XF204 IRT: All versions
  • SCALANCE XF204-2: All versions
  • SCALANCE XF204-2BA IRT: All versions
  • SCALANCE XF206-1: All versions
  • SCALANCE XF208: All versions
  • SIMATIC RF 181 EIP: All versions
  • SIMATIC RF 182C: All versions


There is a DHCP vulnerability in Wind River VxWorks, for versions prior to 6.5. This vulnerability could cause a heap overflow if exploited.
CVE-2021-29998 has been assigned to this vulnerability. A CVSS v3 base score of 9.8 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).




Siemens reported this vulnerability to CISA.


Siemens has identified the following specific workarounds and mitigations users can apply to reduce the risk:

  • Avoid the use of the DHCP client if unnecessary to your environment.
  • If the DHCP client is enabled, it is recommended to disable it.

As a general security measure, Siemens strongly recommends protecting network access to devices with appropriate mechanisms. In order to operate the devices in a protected IT environment, Siemens recommends configuring the environment according to Siemens Operational Guidelines for Industrial Security, and to follow the recommendations in the product manuals.

Additional information on industrial security by Siemens can be found at: https://www.siemens.com/industrialsecurity.

For more information about this vulnerability and the associated remediations, please see Siemens publication number SSA-560465.

CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. Specifically, users should:

  • Minimize network exposure for all control system devices and/or systems, and ensure that they are not accessible from the Internet.
  • Locate control system networks and remote devices behind firewalls, and isolate them from the business network.
  • When remote access is required, use secure methods, such as Virtual Private Networks (VPNs), recognizing that VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize that VPN is only as secure as the connected devices.

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 us-cert.cisa.gov. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.

Additional mitigation guidance and recommended practices are publicly available on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.

Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to CISA for tracking and correlation against other incidents.

No known public exploits specifically target this vulnerability.

Contact Information

For any questions related to this report, please contact the CISA at:

Email: CISAservicedesk@cisa.dhs.gov
Toll Free: 1-888-282-0870

For industrial control systems cybersecurity information:  https://us-cert.cisa.gov/ics 
or incident reporting:  https://us-cert.cisa.gov/report

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