splunk-security_content/docs/_posts/2022-05-02-powershell_creating_thread_mutex.md

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Powershell Creating Thread Mutex	Obfuscated Files or Information , Indicator Removal from Tools , PowerShell	Endpoint	2022-05-02	true		Obfuscated Files or Information Indicator Removal from Tools PowerShell Defense Evasion Defense Evasion 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 using the mutex function. This function is commonly seen in some obfuscated PowerShell scripts to make sure that only one instance of there process is running on a compromise machine. 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

• Last Updated: 2022-05-02

• Author: Teoderick Contreras, Splunk

• ID: 637557ec-ca08-11eb-bd0a-acde48001122

Annotations

ATT&CK

ID	Technique	Tactic
T1027	Obfuscated Files or Information	Defense Evasion

| T1027.005 | Indicator Removal from Tools | Defense Evasion |

| T1059.001 | PowerShell | Execution |

Kill Chain Phase

• Exploitation

NIST

CIS20

CVE

Search

`powershell` EventCode=4104 ScriptBlockText = "*Threading.Mutex*" 
| stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `powershell_creating_thread_mutex_filter`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• powershell

ℹ️ powershell_creating_thread_mutex_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
• ScriptBlockText
• Computer
• UserID

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 developer may used this function in their script for instance checking too.

Associated Analytic story

• Malicious PowerShell

RBA

Risk Score	Impact	Confidence	Message
40.0	50	80	A suspicious powershell script contains Thread Mutex in ScriptBlockText with EventCode EventCode in host Computer

ℹ️ 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://isc.sans.edu/forums/diary/Some+Powershell+Malicious+Code/22988/
• 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/attack_techniques/T1059.001/powershell_script_block_logging/sbl_xml.log

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