|Tactic||Inhibit Response Function|
|Data Sources||Sequential event recorder, Alarm history, Network protocol analysis, Packet capture|
Adversaries may forcibly restart or shutdown a device in the ICS environment to disrupt and potentially cause adverse effects on the physical processes it helps to control. Methods of device restart and shutdown exist as built-in, standard functionalities. This can include interactive device web interfaces, CLIs, and network protocol commands, among others. Device restart or shutdown may also occur as a consequence of changing a device into an alternative mode of operation for testing or firmware loading.
Unexpected restart or shutdown of control system devices may contribute to impact, by preventing expected response functions from activating and being received in critical states. This can also be a sign of malicious device modification, as many updates require a shutdown in order to take affect.1
For example, DNP3's function code 0x0D can reset and reconfigure DNP3 outstations by forcing them to perform a complete power cycle.1
In the 2015 attack on the Ukranian power grid, the adversaries gained access to the control networks of three different energy companies. The adversaries scheduled disconnects for the uniterruptable power supply (UPS) systems so that when power was disconnected from the substations, the devices would shut down and service could not be recovered.2
- The Industroyer SIPROTEC DoS module exploits the CVE-2015-5374 vulnerability in order to render a Siemens SIPROTEC device unresponsive. Once this vulnerability is successfully exploited, the target device stops responding to any commands until it is rebooted manually.3 Once the tool is executed it sends specifically crafted packets to port 50,000 of the target IP addresses using UDP. The UDP packet contains the following 18 byte payload:
0x11 49 00 00 00 00 00 00 00 00 00 00 00 00 00 00 28 9E.3
- Disable or Remove Feature or Program - Ensure remote commands that enable device shutdown are disabled if they are not necessary. Examples include DNP3's 0x0D function code or unnecessary device management functions.
- Authorization Enforcement - All field controllers should restrict the modification of programs to only certain users (e.g., engineers, field technician), preferably through implementing a role-based access mechanism.
- Human User Authentication - All field controllers should require users to authenticate for all remote or local management sessions. The authentication mechanisms should also support Account Use Policies, Password Policies, and User Account Management.
- Communication Authenticity - Protocols used for control functions should provide authenticity through MAC functions or digital signatures. If not, utilize bump-in-the-wire devices or VPNs to enforce communication authenticity between devices that are not capable of supporting this (e.g., legacy controllers, RTUs).
- Network Allowlists - Use host-based allowlists to prevent devices from accepting connections from unauthorized systems. For example, allowlists can be used to ensure devices can only connect with master stations or known management/engineering workstations.4
- Access Management - All devices or systems changes, including all administrative functions, should require authentication. Consider using access management technologies to enforce authorization on all management interface access attempts, especially when the device does not inherently provide strong authentication and authorization functions.
- Software Process and Device Authentication - Authenticate connections from software and devices to prevent unauthorized systems from accessing protected management functions.
- Network Segmentation - Segment operational network and systems to restrict access to critical system functions to predetermined management systems.4
- Filter Network Traffic - Application denylists can be used to block automation protocol functions used to initiate device shutdowns or restarts, such as DNP3's 0x0D function code, or vulnerabilities that can be used to trigger device shutdowns (e.g., CVE-2014-9195, CVE-2015-5374).
- Bonnie Zhu, Anthony Joseph, Shankar Sastry. (2011). A Taxonomy of Cyber Attacks on SCADA Systems. Retrieved January 12, 2018.
- Electricity Information Sharing and Analysis Center; SANS Industrial Control Systems. (2016, March 18). Analysis of the Cyber Attack on the Ukranian Power Grid: Defense Use Case. Retrieved March 27, 2018.