Siemens SIMATIC S7-300 CPU

1. EXECUTIVE SUMMARY

• CVSS v3 7.5
• ATTENTION: Exploitable remotely/low skill level to exploit
• Vendor: Siemens
• Equipment: SIMATIC S7-300 CPU
• Vulnerability: Improper Input Validation

2. RISK EVALUATION

Successful exploitation of this vulnerability could crash the device being accessed, resulting in a denial-of-service condition.

3. TECHNICAL DETAILS

3.1 AFFECTED PRODUCTS

Siemens reports the following SIMATIC S7-300 CPU product is affected: 

• SIMATIC S7-300 CPUs: All versions prior to v3.X.16

3.2 VULNERABILITY OVERVIEW

3.2.1    IMPROPER INPUT VALIDATION CWE-20

The affected CPUs improperly validate S7 communication packets, which could cause a denial-of-service condition of the CPU. The CPU will remain in DEFECT mode until manual restart.

Successful exploitation requires an attacker to send a specially crafted S7 communication packet to a communication interface of the CPU. This includes Ethernet, PROFIBUS, and Multi Point Interfaces (MPI). The vulnerability could allow a denial-of-service condition of the core functionality of the CPU.

CVE-2018-16561 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: Chemical, Critical Manufacturing, Energy, Food and Agriculture, Water and Wastewater Systems
• COUNTRIES/AREAS DEPLOYED: Worldwide
• COMPANY HEADQUARTERS LOCATION: Germany

3.4 RESEARCHER

China Industrial Control Systems Cyber Emergency Response Team (CIC) reported this vulnerability to Siemens.

4. MITIGATIONS

Siemens recommends users update to Version 3.X.16, which can be downloaded from the following link:

https://support.industry.siemens.com/cs/ww/en/ps/13752/dl

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

• Siemens recommends operating the devices only within trusted networks

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 (https://www.siemens.com/cert/operational-guidelines-industrial-security), and following 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 on this vulnerability and associated software updates, please see Siemens security advisory SSA-306710 on their website: 

https://www.siemens.com/cert/advisories

NCCIC 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.

NCCIC reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.

NCCIC also provides a section for control systems security recommended practices on the ICS-CERT web page. 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-CERT website 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 NCCIC for tracking and correlation against other incidents.

No known public exploits specifically target this vulnerability.