Detection: Detect Empire with PowerShell Script Block Logging

Updated Date: 2024-11-13 ID: bc1dc6b8-c954-11eb-bade-acde48001122 Author: Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

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.

Search

1`powershell` EventCode=4104  (ScriptBlockText=*system.net.webclient* AND ScriptBlockText=*frombase64string*) 
2| stats count min(_time) as firstTime max(_time) as lastTime by Opcode Computer UserID EventCode ScriptBlockText 
3| rename UserID as user 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `detect_empire_with_powershell_script_block_logging_filter`

Data Source

Name	Platform	Sourcetype	Source
Powershell Script Block Logging 4104	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-PowerShell/Operational'`

Macros Used

Name	Value
powershell	`(source=WinEventLog:Microsoft-Windows-PowerShell/Operational OR source="XmlWinEventLog:Microsoft-Windows-PowerShell/Operational")`
detect_empire_with_powershell_script_block_logging_filter	`search *`

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

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1059	Command and Scripting Interpreter	Execution
T1059.001	PowerShell	Execution

Installation

DE.CM

CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

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

Risk Based Analytics (RBA)

Risk Message:

The following behavior was identified and typically related to PowerShell-Empire on $Computer$ by $user$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
user	user	81	No Threat Objects
Computer	system	81	No Threat Objects

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-PowerShell/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-PowerShell/Operational`	`XmlWinEventLog`

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: GitHub | Version: 5