Siemens TCP Stack of SIMATIC MV400

1. EXECUTIVE SUMMARY

• CVSS v3 7.5
• ATTENTION: Exploitable remotely/low skill level to exploit
• Vendor: Siemens
• Equipment: SIMATIC MV400
• Vulnerabilities: Improper Validation of Specified Index, Position, or Offset in Input; Use of Insufficiently Random Values

2. RISK EVALUATION

Successful exploitation of these vulnerabilities could cause a denial-of-service condition or affect the integrity of TCP connections.

3. TECHNICAL DETAILS

3.1 AFFECTED PRODUCTS

The following products are affected:

• SIMATIC MV400 family: All versions prior to v7.0.6

3.2 VULNERABILITY OVERVIEW

3.2.1    IMPROPER VALIDATION OF SPECIFIED INDEX, POSITION, OR OFFSET IN INPUT CWE-1285

The underlying TCP stack of the affected products does not correctly validate the sequence number for incoming TCP RST packages. An attacker could exploit this vulnerability to terminate arbitrary TCP sessions.

CVE-2020-25241 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).

3.2.2    USE OF INSUFFICIENTLY RANDOM VALUES CWE-330

ISN generator is initialized with a constant value and has constant increments. An attacker could exploit this vulnerability to predict and hijack TCP sessions.

CVE-2020-27632 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:H/A:N).

3.3 BACKGROUND

• CRITICAL INFRASTRUCTURE SECTORS: Critical Manufacturing
• COUNTRIES/AREAS DEPLOYED: Worldwide
• COMPANY HEADQUARTERS LOCATION: Germany

3.4 RESEARCHER

Siemens reported these vulnerabilities to CISA.

4. MITIGATIONS

Siemens recommends users upgrade affected products to v7.0.6

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.

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

For more information on these vulnerabilities and associated software updates, please see Siemens security advisory SSA-599268

CISA recommends users take defensive measures to minimize the risk of exploitation of these vulnerabilities. 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 these vulnerabilities.