Reaction SCAN command

The Reaction SCAN command defines the ability to perform process scans when a rule matches.

Note

Exploit Prevention is not supported in the ARM architecture.

Description

Note

The Reaction SCAN command is available with Trellix ENS 10.7 November 2020 Update and later.

This command takes two arguments:

Syntax

An example of a rule with the Reaction SCAN command. The command precedes the Process clause in this example of a simple Expert Rule where the Reaction SCAN command is used.

Rule {
    Reaction SCAN ACTOR_PROCESS ScanAction REPORT_CLEAN_DELETE_PROCESS
    Reaction SCAN TARGET_PROCESS ScanAction REPORT_CLEAN_DELETE_PROCESS
    Process {
        Include OBJECT_NAME { -v abc.exe}
    }
    Target {
        Match PROCESS {
            Include OBJECT_NAME { -v xyz.exe}
            Include -access "CREATE"
        }
   }
}

The Reaction SCAN command can also be used in chained Expert Rules. The command is placed at the top of the Next_Process_Behavior clause.

Rule {
    Reaction SCAN ACTOR_PROCESS ScanAction REPORT
    Process {
        Include OBJECT_NAME { -v abc.exe }
    }
    Target {
        Match PROCESS {
            Include OBJECT_NAME { -v xyz.exe }
            Include -access "CREATE"
        }
        Next_Process_Behavior {
         	Reaction SCAN TARGET_PROCESS ScanAction REPORT
	    Target {
                Match PROCESS {
                    Include OBJECT_NAME { -v rmg.exe }
                    Include -access "CREATE"
                }
            }
        }
    }
  }

Example

Reaction SCAN ACTOR_PROCESS ScanAction REPORT_CLEAN_DELETE_PROCESS

When the Expert Rule matches, the actor process is scanned with a scan action that tries to clean the process. If the clean action is not successful, it attempts to delete the process and will log the detection to On-Demand Scan Activity log and report the detection to ePO - On-prem.

Reaction SCAN TARGET_PROCESS ScanAction REPORT  

When the Expert Rule matches, the target process is scanned with a scan action that will log the detection to On-Demand Scan Activity log and report the detection to ePO - On-prem.

For more detailed examples on how to use Reaction SCAN, see Expert rule triggered process scan.

Note

The process scan only works on processes, it does not work on files and registry. The process scan takes around 2 seconds to complete; on a detection the complete scan takes between 2–9 seconds to fix it.

Scan actions

These are the scan actions and their descriptions.

If multiple Reaction SCAN commands are included in an Expert Rule, each command can have a different scan action.

Task-less process scan

When the Expert Rule matches, a process scan request is sent asynchronously to On-Demand Scan. The On-Demand Scan performs the process scan as a Task-less On-Demand Scan. This scan happens immediately and does not depend on the scheduled scan task.

Events and log details

Detection logging

If a detection occurs, the detection is logged in the On-Demand Scan Activity log. The detection information in the log includes the rule ID, rule name which triggered the scan, the name of the detected process, and the scan action (remediation action) taken.

ePO - On-prem events

If one of the report scan actions (REPORT, REPORT_CLEAN_PROCESS, REPORT_DELETE_PROCESS, REPORT_CLEAN_DELETE_PROCESS REPORT) is used, a detection event is sent to ePO - On-prem. The detection event follows the same format as of On-Demand Scan process scan detection events except for the fields Task Name, Analyzer Rule ID, and Analyzer Rule Name.

These fields are named in these format:

Scanned or not scanned log details

Each scan is logged to the On-Demand Scan Debug log. If a scan does not occur for some reason, the rule ID, rule name, process name, and the reason why the scan could not be completed is logged in the On-Demand Scan Activity log.

Debug logging

The complete flow of an Expert Rule triggering a process scan can be seen by enabling debug logging for Exploit Prevention and On-Demand Scan. The Expert Rule sending the scan request is seen in the Exploit Prevention Debug log, and the handling of the process scan is seen in On-Demand Scan Debug log.

Special consideration