Detect Operating Mode

What the technique is

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. 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. Remote - Allows for remote changes to a PLCs operation mode. Stop - The PLC and program is stopped, while in this mode, outputs are forced off. 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. […]

What MITRE says you would watch

• AN1900

  Monitor ICS automation network protocols for functions related to reading an asset’s operating mode. In some cases, there may be multiple ways to detect a device’s operating mode, one of which is typically used in the operational environment. Monitor for the operating mode being checked in unexpected ways.