Utilize/Change Operating Mode

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Utilize/Change Operating Mode
ID T0858
Tactic Evasion, Inhibit Response Function
Data Sources Alarm history, Sequential event recorder, Network protocol analysis, Packet capture
Asset Safety Instrumented System/Protection Relay, Field Controller/RTU/PLC/IED


Adversaries may place controllers into an alternate mode of operation to enable configuration setting changes for evasive code execution or to inhibit device functionality. Programmable controllers typically have several modes of operation. These modes can be broken down into three main categories: program run, program edit, and program write. Each of these modes puts the device in a state in which certain functions are available. For instance, the program edit mode allows alterations to be made to the user program while the device is still online.

By driving a device into an alternate mode of operation, an adversary has the ability to change configuration settings in such a way to cause a Impact to equipment and/or industrial process associated with the targeted device. An adversary may also use this alternate mode to execute arbitrary code which could be used to evade defenses.

Procedure Examples

  • Triton is able to modify code if the Triconex SIS Controller is configured with the physical keyswitch in ‘program mode’ during operation. If the controller is placed in Run mode (program changes not permitted), arbitrary changes in logic are not possible substantially reducing the likelihood of manipulation. Once the Triton implant is installed on the SIS it is able to conduct any operation regardless of any future position of the keyswitch.1.


  • Authorization Enforcement - All field controllers should restrict operating mode changes to only required authenticated users (e.g., engineers, field technicians), preferably through implementing a role-based access mechanism. Further, physical mechanisms (e.g., keys) can also be used to limit unauthorized operating mode changes.
  • Communication Authenticity - Protocols used for device management should authenticate all network messages to prevent unauthorized system changes.
  • 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.2
  • Access Management - Authenticate all access to field controllers before authorizing access to, or modification of, a device's state, logic, or programs. Centralized authentication techniques can help manage the large number of field controller accounts needed across the ICS.
  • Network Segmentation - Segment operational network and systems to restrict access to critical system functions to predetermined management systems.2