splunk-security_content/docs/_posts/2021-06-10-powershell_processing_stream_of_data.md

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title	excerpt	categories	last_modified_at	toc	toc_label	tags
Powershell Processing Stream Of Data	Command and Scripting Interpreter , PowerShell	Endpoint	2021-06-10	true		Command and Scripting Interpreter PowerShell Execution Execution Splunk Enterprise Splunk Enterprise Security Splunk Cloud

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Description

The following analytic identifies suspicious PowerShell script execution via EventCode 4104 that is processing compressed stream data. This is typically found in obfuscated PowerShell or PowerShell executing embedded .NET or binary files that are stream flattened and will be deflated durnig execution. During triage, review parallel processes within the same timeframe. Review the full script block to identify other related artifacts.

• Type: TTP
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel:
• Last Updated: 2021-06-10
• Author: Teoderick Contreras, Splunk
• ID: 0d718b52-c9f1-11eb-bc61-acde48001122

ATT&CK

ID	Technique	Tactic
T1059	Command and Scripting Interpreter	Execution

| T1059.001 | PowerShell | Execution |

Search

`powershell` EventCode=4104 Message = "*IO.Compression.*" OR Message = "*IO.StreamReader*" OR Message = "*]::Decompress*" 
| stats count min(_time) as firstTime max(_time) as lastTime by EventCode Message ComputerName User 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `powershell_processing_stream_of_data_filter`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• powershell

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

Required field

• _time
• EventCode
• Message
• ComputerName
• User
• Score

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

powershell may used this function to process compressed data.

Associated Analytic story

• Malicious PowerShell

Kill Chain Phase

• Exploitation

RBA

Risk Score	Impact	Confidence	Message
40.0	50	80	A suspicious powershell script contains stream command in Message commonly for processing compressed or to decompressed binary file with EventCode EventCode in host ComputerName

Reference

• https://medium.com/@ahmedjouini99/deobfuscating-emotets-powershell-payload-e39fb116f7b9
• 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/

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/honeypots/pwsh/windows-powershell.log

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