Unauthorized Command Message

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Unauthorized Command Message
ID T0855
Tactic Impair Process Control
Data Sources Alarm history, Sequential event recorder, Netflow/Enclave netflow, Network protocol analysis, Packet capture
Asset Field Controller/RTU/PLC/IED


Adversaries may send unauthorized command messages to instruct control systems devices to perform actions outside their expected functionality for process control. 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 2015 attack on the Ukranian power grid, the adversaries gained access to the control networks of three different energy companies. The adversaries used valid credentials to seize control of operator workstations and access a distribution management system (DMS) client application via a VPN. The adversaries used these tools to issue unauthorized commands to breakers at substations which caused a loss of power to over 225,000 customers over various areas.3

Procedure Examples

  • The Industroyer IEC 101 module has the capability to communicate with devices (likely RTUs) via the IEC 101 protocol. The module will attempt to find all Information Object Addresses (IOAs) for the device and attempt to change their state in the following sequence: OFF, ON, OFF.4
  • In states 3 and 4 Stuxnet sends two network bursts (done through the DP_SEND primitive). The data in the frames are instructions for the frequency converter drives.5
  • Using Triton, an adversary can manipulate the process into an unsafe state from the DCS while preventing the SIS from functioning appropriately.6


  • 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.7
  • 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.89710
  • 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.