Detection: Windows PowerShell Script Block With Malicious String

Updated Date: 2024-12-19 ID: 0f09cedd-10f1-4b9f-bdea-7a8b06ea575d Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the execution of multiple offensive toolkits and commands by leveraging PowerShell Script Block Logging (EventCode=4104). This method captures and logs the full command sent to PowerShell, allowing for the identification of suspicious activities including several well-known tools used for credential theft, lateral movement, and persistence. If confirmed malicious, this could lead to unauthorized access, privilege escalation, and potential compromise of sensitive information within the environment.

 1`powershell` ScriptBlockText EventCode=4104
 2
 3| stats count min(_time) as firstTime max(_time) as lastTime list(ScriptBlockText) as command Values(OpCode) as reason values(Path) as file_name values(UserID) as user by ActivityID, Computer, EventCode 
 4
 5| eval command = mvjoin(command,"\n"), dest = Computer, signature = EventCode, signature_id = ActivityID
 6
 7| lookup malicious_powershell_strings command  
 8
 9| where isnotnull(match)
10
11| `security_content_ctime(firstTime)` 
12
13| `security_content_ctime(lastTime)`
14
15| `windows_powershell_script_block_with_malicious_string_filter`

Data Source

Name Platform Sourcetype Source
Powershell Script Block Logging 4104 Windows icon 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" OR source=WinEventLog:PowerShellCore/Operational OR source="XmlWinEventLog:PowerShellCore/Operational")
windows_powershell_script_block_with_malicious_string_filter search *
windows_powershell_script_block_with_malicious_string_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
T1059.001 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

The following analytic requires PowerShell operational logs to be imported. Modify the powershell macro as needed to match the sourcetype or add index. This analytic is specific to 4104, or PowerShell Script Block Logging.

Known False Positives

Unknown, possible usage by internal red team or powershell commands with overlap.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The user $user$ ran a known malicious PowerShell string matching $match$ on $dest$

Risk Object Risk Object Type Risk Score Threat Objects
dest system 70 signature_id
user user 70 signature_id

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: 1