Adversaries may modify alarm settings to prevent alerts that may inform operators of their presence or to prevent responses to dangerous and unintended scenarios. Reporting messages are a standard part of data acquisition in control systems. Reporting messages are used as a way to transmit system state information and acknowledgements that specific actions have occurred. These messages provide vital information for the management of a physical process, and keep operators, engineers, and administrators aware of the state of system devices and physical processes. If an adversary is able to change the reporting settings, certain events could be prevented from being reported. This type of modification can also prevent operators or devices from performing actions to keep the system in a safe state. If critical reporting messages cannot trigger these actions then a [Impact](https://attack.mitre.org/tactics/TA0105) could occur. In ICS environments, the adversary may have to use [Alarm Suppression](https://attack.mitre.org/techniques/T0878) or contend with multiple alarms and/or alarm propagation to achieve a specific goal to evade detection or prevent intended responses from occurring. (Citation: Jos Wetzels, Marina Krotofil 2019) Methods of suppression often rely on modification of alarm settings, such as modifying in memory code to fixed values or tampering with assembly level instruction code.
Require user authentication before allowing access to data or accepting commands to a device. While strong multi-factor authentication is preferable, it is not always feasible within ICS environments. Performing strong user authentication also requires additional security controls and processes which are often the target of related adversarial techniques (e.g., Valid Accounts, Default Credentials). Therefore, associated ATT&CK mitigations should be considered in addition to this, including [Multi-factor Authentication](https://attack.mitre.org/mitigations/M0932), [Account Use Policies](https://attack.mitre.org/mitigations/M0936), [Password Policies](https://attack.mitre.org/mitigations/M0927), [User Account Management](https://attack.mitre.org/mitigations/M0918), [Privileged Account Management](https://attack.mitre.org/mitigations/M0926), and [User Account Control](https://attack.mitre.org/mitigations/M1052).
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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