Unauthorized Command Message

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Unauthorized Command Message
Technique
ID T0855
Tactic Impair Process Control
Data Sources Network Traffic: Network Traffic Content, Application Log: Application Log Content, Operational Databases: Process History/Live Data, Operational Databases: Process/Event Alarm
Asset Field Controller/RTU/PLC/IED

Description

Adversaries may send unauthorized command messages to instruct control system assets to perform actions outside of their intended functionality, or without the logical preconditions to trigger their expected function. Command messages are used in ICS networks to give direct instructions to control systems devices. If an adversary can send an unauthorized command message to a control system, then it can instruct the control systems device to perform an action outside the normal bounds of the device's actions. An adversary could potentially instruct a control systems device to perform an action that will cause an Impact.1

In the Maroochy Attack, the adversary used a dedicated analog two-way radio system to send false data and instructions to pumping stations and the central computer.2

In the Dallas Siren incident, adversaries were able to send command messages to activate tornado alarm systems across the city without an impending tornado or other disaster.34


Procedure Examples

  • In the Ukraine 2015 Incident, Sandworm Team issued unauthorized commands to substation breakers after gaining control of operator workstations and accessing a distribution management system (DMS) client application.5
  • Using its protocol payloads, Industroyer sends unauthorized commands to RTUs to change the state of equipment.6
  • Stuxnet sends two network bursts (done through the DP_SEND primitive). The data in the frames are instructions for the frequency converter drives.7

Mitigations

  • 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.8
  • Network Segmentation - Segment operational assets and their management devices based on their functional role within the process. Enabling more strict isolation to more critical control and operational information within the control environment.910811
  • Filter Network Traffic - Perform inline allowlisting of automation protocol commands to prevent devices from sending unauthorized command or reporting messages. Allow/denylist techniques need to be designed with sufficient accuracy to prevent the unintended blocking of valid messages.


References