Adversaries may block access to serial COM to prevent instructions or configurations from reaching target devices. Serial Communication ports (COM) allow communication with control system devices. Devices can receive command and configuration messages over such serial COM. Devices also use serial COM to send command and reporting messages. Blocking device serial COM may also block command messages and block reporting messages.
A serial to Ethernet converter is often connected to a serial COM to facilitate communication between serial and Ethernet devices. One approach to blocking a serial COM would be to create and hold open a TCP session with the Ethernet side of the converter. A serial to Ethernet converter may have a few ports open to facilitate multiple communications. For example, if there are three serial COM available -- 1, 2 and 3 --, the converter might be listening on the corresponding ports 20001, 20002, and 20003. If a TCP/IP connection is opened with one of these ports and held open, then the port will be unavailable for use by another party. One way the adversary could achieve this would be to initiate a TCP session with the serial to Ethernet converter at 10.0.0.1 via Telnet on serial port 1 with the following command: telnet 10.0.0.1 20001.
| ID | Name | Description |
|---|---|---|
| C0028 | 2015 Ukraine Electric Power Attack |
During the 2015 Ukraine Electric Power Attack, Sandworm Team overwrote the serial-to-ethernet converter firmware, rendering the devices not operational. This meant that communication to the downstream serial devices was either not possible or more difficult. [1] |
| S0604 | Industroyer |
In Industroyer the first COM port from the configuration file is used for the actual communication and the two other COM ports are just opened to prevent other processes accessing them. Thus, the IEC 101 payload component is able to take over and maintain control of the RTU device. [2] |
| ID | Mitigation | Description |
|---|---|---|
| M0807 | Network Allowlists |
Implement network allowlists to minimize serial comm port access to only authorized hosts, such as comm servers and RTUs. |
| M0930 | Network Segmentation |
Restrict unauthorized devices from accessing serial comm ports. |
| M0810 | Out-of-Band Communications Channel |
Ensure devices have an alternative method for communicating in the event that a valid COM port is unavailable. |
| ID | Name | Analytic ID | Analytic Description |
|---|---|---|---|
| DET0797 | Detection of Block Serial COM | AN1929 |
Real-time monitoring identifies a loss of communication with serially-connected field devices correlated with a configuration change event on the serial-to-Ethernet gateway. Documented in the 2015 Ukraine attack, where Sandworm used malicious firmware to render serial-to-Ethernet converters inoperable. OT operational-fidelity gate: Alert only when the action is not attributable to an authorized operator/engineering source for the specific target and function, and it is either outside an approved change/maintenance window or lacks matching change-control context; where telemetry permits, require corroborating device, configuration, or process-state effect. Suppress activity that fully matches approved maintenance, commissioning, failover, recovery, or tested control procedures. |
| AN2119 |
Real-time monitoring identifies writes to serial device configuration files or |
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| AN2200 |
Real-time monitoring identifies configuration changes to serial server or terminal server devices that alter serial port parameters for ports connected to field devices. OT operational-fidelity gate: Alert only when the action is not attributable to an authorized operator/engineering source for the specific target and function, and it is either outside an approved change/maintenance window or lacks matching change-control context; where telemetry permits, require corroborating device, configuration, or process-state effect. Suppress activity that fully matches approved maintenance, commissioning, failover, recovery, or tested control procedures. |
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| AN2280 |
Real-time monitoring identifies Windows serial port configuration changes on Industrial Control System (ICS) gateway hosts that would disrupt communication with serial field devices. OT operational-fidelity gate: Alert only when the action is not attributable to an authorized operator/engineering source for the specific target and function, and it is either outside an approved change/maintenance window or lacks matching change-control context; where telemetry permits, require corroborating device, configuration, or process-state effect. Suppress activity that fully matches approved maintenance, commissioning, failover, recovery, or tested control procedures. |