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Description

The following analytic identifies the use of the EncodedCommand PowerShell parameter. This is typically used by Administrators to run complex scripts, but commonly used by adversaries to hide their code.
The analytic identifies all variations of EncodedCommand, as PowerShell allows the ability to shorten the parameter. For example enc, enco, encod and so forth. In addition, through our research it was identified that PowerShell will interpret different command switch types beyond the hyphen. We have added endash, emdash, horizontal bar, and forward slash.
During triage, review parallel events to determine legitimacy. Tune as needed based on admin scripts in use.
Alternatively, may use regex per matching here https://regexr.com/662ov.

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2021-10-05
  • Author: David Dorsey, Michael Haag, Splunk
  • ID: c4db14d9-7909-48b4-a054-aa14d89dbb19

ATT&CK

ID Technique Tactic
T1027 Obfuscated Files or Information Defense Evasion

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_powershell` by Processes.user Processes.process_name Processes.process Processes.parent_process_name Processes.original_file_name Processes.dest Processes.process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| where match(process,"(?i)[\-
|\/
|–
|—
|―]e(nc*o*d*e*d*c*o*m*m*a*n*d*)*\s+[^-]") 
| `malicious_powershell_process___encoded_command_filter`

Associated Analytic Story

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Required field

  • _time
  • Processes.process_name
  • Processes.process
  • Processes.user
  • Processes.parent_process_name
  • Processes.dest
  • Processes.process_id

Kill Chain Phase

  • Command and Control
  • Actions on Objectives

Known False Positives

System administrators may use this option, but it's not common.

RBA

Risk Score Impact Confidence Message
35.0 70 50 Powershell.exe running potentially malicious encodede commands on $dest$

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 6