Modify Controller Tasking
Where this stands
No Sigma rule can address this — the telemetry MITRE names has no Sigma logsource behind it.
Sigma has no logsource taxonomy for ICS. MITRE's telemetry here is operational historians and controller state, which no Sigma rule can address.
What the technique is
Adversaries may modify the tasking of a controller to allow for the execution of their own programs. This can allow an adversary to manipulate the execution flow and behavior of a controller. According to 61131-3, the association of a Task with a Program Organization Unit (POU) defines a task association. An adversary may modify these associations or create new ones to manipulate the execution flow of a controller. Modification of controller tasking can be accomplished using a Program Download in addition to other types of program modification such as online edit and program append. Tasks have properties, such as interval, frequency and priority to meet the requirements of program execution. Some controller vendors implement tasks with implicit, pre-defined properties whereas others allow for these properties to be formulated explicitly. An adversary may associate their program with tasks that have a higher priority or execute associated programs more frequently. For instance, to ensure cyclic execution of their program on a Siemens controller, an adversary may add their program to the task, Organization Block 1 (OB1).
Read it on attack.mitre.orgWhat MITRE says you would watch
- AN1874
Monitor asset application logs for information that indicate task parameters have changed. Monitor device alarms that indicate controller task parameters have changed, although not all devices produce such alarms. Program Download may be used to enable this technique. Monitor for program downloads which may be noticeable via operational alarms. Asset management systems should be consulted to understand expected program versions. Engineering and asset management software will often maintain a copy of the expected program loaded on a controller and may also record any changes made to controller programs and tasks. Data from these platforms can be used to identify modified controller tasking.
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