ICS Advisory (ICSA-21-068-03)

Siemens SCALANCE and RUGGEDCOM Devices (Update A)

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1. EXECUTIVE SUMMARY

  • CVSS v3 8.8
  • ATTENTION: Exploitable remotely/low attack complexity
  • Vendor: Siemens
  • Equipment: SCALANCE and RUGGEDCOM Devices
  • Vulnerability: Stack-based Buffer Overflow

2. UPDATE INFORMATION

This updated advisory is a follow-up to the original advisory titled ICSA-21-068-03 Siemens SCALANCE and RUGGEDCOM Devices that was published March 9, 2021, to the ICS webpage on us-cert.cisa.gov.

3. RISK EVALUATION

Successful exploitation of this vulnerability could allow an attacker to cause a reboot. Under specific circumstances, an attacker could also achieve remote code execution of the affected devices.

4. TECHNICAL DETAILS

4.1 AFFECTED PRODUCTS

The following Siemens products are affected:

--------- Begin Update A Part 1 of 2 --------

  • RUGGEDCOM RM1224: All versions from v4.3 and prior to v4.6
  • SCALANCE M-800: All versions from v4.3 and prior to v4.6
  • SCALANCE S615: All versions from v4.3 and prior to v4.6
  • SCALANCE XR-300WG: All versions prior to v4.1
  • SCALANCE XB-200: All versions prior to v4.1
  • SCALANCE XC-200: All versions prior to v4.1
  • SCALANCE XF-200BA: All versions prior to v4.1
  • SCALANCE XP-200: All versions prior to v4.1

--------- End Update A Part 1 of 2 --------

  • SCALANCE SC-600 Family: All versions from v2.0 and prior to v2.1.3
  • SCALANCE XM400: All versions prior to v6.2
  • SCALANCE XR500: All versions prior to v6.2

4.2 VULNERABILITY OVERVIEW

4.2.1    STACK-BASED BUFFER OVERFLOW CWE-121

Affected devices contain a stack-based buffer overflow vulnerability in the handling of Spanning Tree Protocol (STP) Bridge Protocol Data Unit (BPDU) frames that could allow a remote attacker to trigger a denial-of-service condition or potential remote code execution. Successful exploitation requires the passive listening feature of the device to be active.

CVE-2021-25667 has been assigned to this vulnerability. A CVSS v3 base score of 8.8 has been calculated; the CVSS vector string is (AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

4.3 BACKGROUND

  • CRITICAL INFRASTRUCTURE SECTORS: Multiple Sectors
  • COUNTRIES/AREAS DEPLOYED: Worldwide
  • COMPANY HEADQUARTERS LOCATION: Germany

4.4 RESEARCHER

Siemens reported this vulnerability to CISA.

5. MITIGATIONS

Siemens recommends applying updates where applicable:

--------- Begin Update A Part 2 of 2 --------

--------- End Update A Part 2 of 2 --------

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

  • Deactivate the STP passive listening feature of the vulnerable devices.

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 following the recommendations in the product manuals.

For additional information, please refer to Siemens Security Advisory SSA-979775

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 VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize 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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