1. EXECUTIVE SUMMARY
- CVSS v3 6.5
- ATTENTION: Exploitable remotely/low skill level to exploit
- Vendor: Siemens
- Equipment: PLUSCONTROL
- Vulnerability: Predictable Exact Value from Previous Values
2. RISK EVALUATION
Successful exploitation of this vulnerability could affect integrity of TCP connections.
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
Siemens reports the vulnerability affects the following products:
- PLUSCONTROL 1st Gen: all versions
3.2 VULNERABILITY OVERVIEW
Initial sequence numbers (ISNs) for TCP connections are derived from an insufficiently random source. As a result, the ISN of current and future TCP connections could be predictable. An attacker could hijack existing sessions or spoof future ones.
- CRITICAL INFRASTRUCTURE SECTORS: Energy
- COUNTRIES/AREAS DEPLOYED: Worldwide
- COMPANY HEADQUARTERS LOCATION: Germany
Siemens reported this vulnerability to CISA.
Siemens has identified the following specific workarounds and mitigations users can apply to reduce risk:
- PLUSCONTROL devices are typically located in a separate LAN segment of energy transmission solutions, where an attacker could use this vulnerability to disrupt SER messages or trace functionalities. Therefore, review the status of the defense-in-depth recommendations that apply to your specific deployment and align as needed; especially the measures on the network layer to prevent accessibility from other network segments.
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 this vulnerability and associated software updates, please see Siemens security advisory SSA-344238
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.