Detect Empire with PowerShell Script Block Logging

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Description

The following analytic detects suspicious PowerShell execution indicative of PowerShell-Empire activity. It leverages PowerShell Script Block Logging (EventCode=4104) to capture and analyze commands sent to PowerShell, specifically looking for patterns involving system.net.webclient and base64 encoding. This behavior is significant as it often represents initial stagers used by PowerShell-Empire, a known post-exploitation framework. If confirmed malicious, this activity could allow attackers to download and execute additional payloads, leading to potential code execution, data exfiltration, or further compromise of the affected system.

• Type: TTP

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2024-05-11
• 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

• Installation

NIST

• DE.CM

CIS20

• CIS 10

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

• Malicious PowerShell
• Hermetic Wiper
• Data Destruction

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

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