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Description

The following analytic utilizes PowerShell Script Block Logging (EventCode=4104) to identify suspicious PowerShell execution. Script Block Logging captures the command sent to PowerShell, the full command to be executed. Upon enabling, logs will output to Windows event logs. Dependent upon volume, enable on critical endpoints or all.
This analytic identifies the common PowerShell stager used by PowerShell-Empire. Each stager that may use PowerShell all uses the same pattern. The initial HTTP will be base64 encoded and use system.net.webclient. Note that some obfuscation may evade the analytic.
During triage, review parallel processes using an EDR product or 4688 events. It will be important to understand the timeline of events around this activity. Review the entire logged PowerShell script block.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel:
  • Last Updated: 2021-06-09
  • Author: Michael Haag, Splunk
  • ID: bc1dc6b8-c954-11eb-bade-acde48001122

ATT&CK

ID Technique Tactic
T1059 Command and Scripting Interpreter Execution
T1059.001 PowerShell Execution
`powershell` EventCode=4104  (Message=*system.net.webclient* AND Message=*frombase64string*) 
| stats count min(_time) as firstTime max(_time) as lastTime by OpCode ComputerName User EventCode Message 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `detect_empire_with_powershell_script_block_logging_filter`

Associated Analytic Story

How To Implement

To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.

Required field

  • _time
  • Message
  • OpCode
  • ComputerName
  • User
  • EventCode

Kill Chain Phase

  • Exploitation

Known False Positives

False positives may only pertain to it not being related to Empire, but another framework. Filter as needed if any applications use the same pattern.

RBA

Risk Score Impact Confidence Message
81.0 90 90 The following behavior was identified and typically related to PowerShell-Empire on $ComputerName$ by $User$.

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

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