Adversaries may target protection function alarms to prevent them from notifying operators of critical conditions. Alarm messages may be a part of an overall reporting system and of particular interest for adversaries. Disruption of the alarm system does not imply the disruption of the reporting system as a whole.
A Secura presentation on targeting OT notes a dual fold goal for adversaries attempting alarm suppression: prevent outgoing alarms from being raised and prevent incoming alarms from being responded to. [1] The method of suppression may greatly depend on the type of alarm in question:
In ICS environments, the adversary may have to suppress or contend with multiple alarms and/or alarm propagation to achieve a specific goal to evade detection or prevent intended responses from occurring. [1] Methods of suppression may involve tampering or altering device displays and logs, modifying in memory code to fixed values, or even tampering with assembly level instruction code.
| ID | Name | Description |
|---|---|---|
| C0020 | Maroochy Water Breach |
In the Maroochy Water Breach, the adversary suppressed alarm reporting to the central computer.[2] |
| ID | Mitigation | Description |
|---|---|---|
| M0807 | Network Allowlists |
Utilize network allowlists to restrict unnecessary connections to network devices (e.g., comm servers, serial to ethernet converters) and services, especially in cases when devices have limits on the number of simultaneous sessions they support. |
| M0930 | Network Segmentation |
Segment operational assets and their management devices based on their functional role within the process. Enabling more strict isolation to more critical control and operational information within the control environment. [3] [4] [5] [6] |
| M0810 | Out-of-Band Communications Channel |
Provide an alternative method for alarms to be reported in the event of a communication failure. |
| M0814 | Static Network Configuration |
Unauthorized connections can be prevented by statically defining the hosts and ports used for automation protocol connections. |
| ID | Name | Analytic ID | Analytic Description |
|---|---|---|---|
| DET0728 | Detection of Alarm Suppression | AN1861 |
Real-time monitoring of the alarm and process historian layer identifies an alarm status transitioning to suppressed, shelved, disabled, or acknowledged without a corresponding operator action recorded within a grace period, correlated with Industrial Control System (ICS) protocol write traffic to alarm configuration or threshold registers arriving in the same window from a source not in the approved engineering list. 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. |
| AN2107 |
Real-time monitoring identifies a write to alarm configuration files on a Linux-based Supervisory Control and Data Acquisition (SCADA)/alarm server by a User Identifier (UID) that is not the alarm management service, or the alarm management service process receiving Application Programming Interface (API) calls that suppress alarm classes without a corresponding operator session. 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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| AN2108 |
Real-time monitoring identifies a write to alarm configuration files or database tables on an Human-Machine Interface (HMI)/alarm server by a process other than the recognized alarm management application, or an alarm-class-disable Application Programming Interface (API) call logged without a corresponding operator session ID in the HMI audit trail. 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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| AN2188 |
Real-time monitoring identifies a network-device ACL, filter, or rate-limit policy change that suppresses or blocks ICS alarm-notification traffic outside the approved network-change baseline. 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. |