ICS Advisory (ICSA-21-131-12)

Siemens SIMATIC SmartVNC HMI WinCC Products

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1. EXECUTIVE SUMMARY

  • CVSS v3 9.8
  • ATTENTION: Exploitable remotely
  • Vendor: Siemens
  • Equipment: SIMATIC HMIs/WinCC Products
  • Vulnerabilities: Access of Memory Location After End of Buffer, Improper Handling of Exceptional Conditions, Improper Restriction of Operations within the Bounds of a Memory Buffer, Uncontrolled Resource Consumption

2. RISK EVALUATION

Successful exploitation of these vulnerabilities could allow remote code execution, information disclosure and denial of service attacks under certain conditions.

3. TECHNICAL DETAILS

3.1 AFFECTED PRODUCTS

The following Siemens SIMATIC HMIs/WinCC products are affected:

  • SIMATIC HMI Comfort Outdoor Panels 7’ and 15’ (incl. SIPLUS variants): All versions prior to v16 Update 4
  • SIMATIC HMI Comfort Panels 4’-22’ (incl. SIPLUS variants): All versions prior to v16 Update 4
  • SIMATIC HMI KTP Mobile Panels KTP400F, KTP700, KTP700F, KTP900, KTP900F: All versions prior to v16 Update 4
  • SIMATIC WinCC Runtime Advanced: All versions prior to v16 Update 4

3.2 VULNERABILITY OVERVIEW

3.2.1    ACCESS OF MEMORY LOCATION AFTER END OF BUFFER CWE-788

SmartVNC has an out-of-bounds memory access vulnerability that could be triggered on the server side when sending data from the client, which could result in a denial-of-service condition.

CVE-2021-25660 has been assigned to this vulnerability. A CVSS v3 base score of 5.4 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:N/A:H).

3.2.2    ACCESS OF MEMORY LOCATION AFTER END OF BUFFER CWE-788

SmartVNC has an out-of-bounds memory access vulnerability that could be triggered on the client side when sending data from the server, which could result in a denial-of-service condition.

CVE-2021-25661 has been assigned to this vulnerability. A CVSS v3 base score of 5.9 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H).

3.2.3    IMPROPER HANDLING OF EXCEPTIONAL CONDITIONS CWE-755

SmartVNC client fails to handle an exception properly if the program execution process is modified after sending a packet from the server, which could result in a denial-of-service condition.

CVE-2021-25662 has been assigned to this vulnerability. A CVSS v3 base score of 5.9 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H).

3.2.4    IMPROPER RESTRICTION OF OPERATIONS WITHIN THE BOUNDS OF A MEMORY BUFFER CWE-119

SmartVNC has a heap allocation leak vulnerability in the server Tight encoder, which could result in a denial-of-service condition.

CVE-2021-27383 has been assigned to this vulnerability. A CVSS v3 base score of 7.5 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

3.2.5    ACCESS OF MEMORY LOCATION AFTER END OF BUFFER CWE-788

SmartVNC has an out-of-bounds memory access vulnerability in the device layout handler represented by a binary data stream on client side, which could result in code execution.

CVE-2021-27384 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).

3.2.6    UNCONTROLLED RESOURCE CONSUMPTION CWE-400

A remote attacker could send specially crafted packets to a SmartVNC device layout handler on the client side, which could influence the number of resources consumed and result in a denial-of-service condition (infinite loop).

CVE-2021-27385 has been assigned to this vulnerability. A CVSS v3 base score of 7.5 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

3.2.7    IMPROPER RESTRICTION OF OPERATIONS WITHIN THE BOUNDS OF A MEMORY BUFFER CWE-119

SmartVNC has a heap allocation leak vulnerability in the device layout handler on client side, which could result in a denial-of-service condition.

CVE-2021-27386 has been assigned to this vulnerability. A CVSS v3 base score of 7.5 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

3.3 BACKGROUND

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

3.4 RESEARCHER

Siemens reported these vulnerabilities to CISA.

4. MITIGATIONS

Siemens recommends applying updates where available:

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

  • Restrict access to Port 5900/TCP to trusted IP addresses only

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 the Siemens operational guidelines for industrial security and following the recommendations in the product manuals.

For additional information, please refer to Siemens Security Advisory SSA-538778

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 its 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.


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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