Adversaries may setup a rogue master to leverage control server functions to communicate with outstations. A rogue master can be used to send legitimate control messages to other control system devices, affecting processes in unintended ways. It may also be used to disrupt network communications by capturing and receiving the network traffic meant for the actual master. Impersonating a master may also allow an adversary to avoid detection. In the case of the 2017 Dallas Siren incident, adversaries used a rogue master to send command messages to the 156 distributed sirens across the city, either through a single rogue transmitter with a strong signal, or using many distributed repeaters. (Citation: Bastille April 2017) (Citation: Zack Whittaker April 2017)
Use network appliances to filter ingress or egress traffic and perform protocol-based filtering. Configure software on endpoints to filter network traffic. Perform inline allow/denylisting of network messages based on the application layer (OSI Layer 7) protocol, especially for automation protocols. Application allowlists are beneficial when there are well-defined communication sequences, types, rates, or patterns needed during expected system operations. Application denylists may be needed if all acceptable communication sequences cannot be defined, but instead a set of known malicious uses can be denied (e.g., excessive communication attempts, shutdown messages, invalid commands). Devices performing these functions are often referred to as deep-packet inspection (DPI) firewalls, context-aware firewalls, or firewalls blocking specific automation/SCADA protocol aware firewalls. (Citation: Centre for the Protection of National Infrastructure February 2005)
M0930Network SegmentationArchitect sections of the network to isolate critical systems, functions, or resources. Use physical and logical segmentation to prevent access to potentially sensitive systems and information. Use a DMZ to contain any internet-facing services that should not be exposed from the internal network. Restrict network access to only required systems and services. In addition, prevent systems from other networks or business functions (e.g., enterprise) from accessing critical process control systems. For example, in IEC 62443, systems within the same secure level should be grouped into a zone, and access to that zone is restricted by a conduit, or mechanism to restrict data flows between zones by segmenting the network. (Citation: IEC February 2019) (Citation: IEC August 2013)
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