Detect Empire with PowerShell Script Block Logging

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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

• Last Updated: 2022-02-24
• Author: Michael Haag, Splunk
• ID: bc1dc6b8-c954-11eb-bade-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1059	Command and Scripting Interpreter	Execution

T1059.001

PowerShell

Execution

Kill Chain Phase

• Exploitation

NIST

CIS20

CVE

Search

`powershell` EventCode=4104  (ScriptBlockText=*system.net.webclient* AND ScriptBlockText=*frombase64string*) 
| stats count min(_time) as firstTime max(_time) as lastTime by Opcode Computer UserID EventCode ScriptBlockText 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `detect_empire_with_powershell_script_block_logging_filter`

Macros

The SPL above uses the following Macros:

• powershell
• security_content_ctime

detect_empire_with_powershell_script_block_logging_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

• _time
• ScriptBlockText
• Opcode
• Computer
• UserID
• EventCode

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.

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.

Associated Analytic Story

• Hermetic Wiper
• Malicious PowerShell

RBA

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

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.
• https://blog.palantir.com/tampering-with-windows-event-tracing-background-offense-and-defense-4be7ac62ac63
• https://static1.squarespace.com/static/552092d5e4b0661088167e5c/t/59c1814829f18782e24f1fe2/1505853768977/Windows+PowerShell+Logging+Cheat+Sheet+ver+Sept+2017+v2.1.pdf
• https://www.crowdstrike.com/blog/investigating-powershell-command-and-script-logging/
• https://github.com/BC-SECURITY/Empire
• https://www.splunk.com/en_us/blog/security/hunting-for-malicious-powershell-using-script-block-logging.html

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059.001/powershell_script_block_logging/empire.log

source | version: 2