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T0868 Detect Operating Mode

Adversaries may gather information about a PLCs or controllers current operating mode. Operating modes dictate what change or maintenance functions can be manipulated and are often controlled by a key switch on the PLC (e.g., run, prog [program], and remote). Knowledge of these states may be valuable to an adversary to determine if they are able to reprogram the PLC. Operating modes and the mechanisms by which they are selected often vary by vendor and product line. Some commonly implemented operating modes are described below:

  • Program - This mode must be enabled before changes can be made to a devices program. This allows program uploads and downloads between the device and an engineering workstation. Often the PLCs logic Is halted, and all outputs may be forced off. 2
  • Run - Execution of the devices program occurs in this mode. Input and output (values, points, tags, elements, etc.) are monitored and used according to the programs logic.Program Upload and Program Download are disabled while in this mode. 3 1 2 4
  • Remote - Allows for remote changes to a PLCs operation mode. 4
  • Stop - The PLC and program is stopped, while in this mode, outputs are forced off. 1
  • Reset - Conditions on the PLC are reset to their original states. Warm resets may retain some memory while cold resets will reset all I/O and data registers. 1
  • Test / Monitor mode - Similar to run mode, I/O is processed, although this mode allows for monitoring, force set, resets, and more generally tuning or debugging of the system. Often monitor mode may be used as a trial for initialization. 3
Item Value
ID T0868
Sub-techniques
Tactics TA0100
Platforms Field Controller/RTU/PLC/IED
Version 1.0
Created 21 May 2020
Last Modified 09 March 2023

Procedure Examples

ID Name Description
S1009 Triton Triton contains a file named TS_cnames.py which contains default definitions for program state (TS_progstate). Program state is referenced in TsHi.py.6

Mitigations

ID Mitigation Description
M0801 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.
M0800 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.
M0802 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).
M0937 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.
M0804 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.
M0807 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. 5
M0930 Network Segmentation Segment operational network and systems to restrict access to critical system functions to predetermined management systems. 5
M0813 Software Process and Device Authentication Authenticate connections from software and devices to prevent unauthorized systems from accessing protected management functions.

Detection

ID Data Source Data Component
DS0029 Network Traffic Network Traffic Content

References

  1. Machine Information Systems 2007 How PLCs Work Retrieved. 2021/01/28  ↩↩↩

  2. N.A. 2017, October What are the different operating modes in PLC? Retrieved. 2021/01/28  ↩↩

  3. Omron Machine Information Systems 2007 How PLCs Work Retrieved. 2021/01/28 PLC Different Operating Modes Retrieved. 2021/01/28  ↩↩

  4. PLCgurus 2021 PLC Basics Modes Of Operation Retrieved. 2021/01/28  ↩↩

  5. Department of Homeland Security 2016, September Retrieved. 2020/09/25  ↩↩

  6. MDudek-ICS TRISIS-TRITON-HATMAN Retrieved. 2019/11/03  ↩