name: Powershell Creating Thread Mutex
id: 637557ec-ca08-11eb-bd0a-acde48001122
version: 5
date: '2024-09-30'
author: Teoderick Contreras, Splunk
status: production
type: TTP
description: The following analytic detects the execution of PowerShell scripts using the `mutex` function via EventCode 4104. This detection leverages PowerShell Script Block Logging to identify scripts that create thread mutexes, a technique often used in obfuscated scripts to ensure only one instance runs on a compromised machine. This activity is significant as it may indicate the presence of sophisticated malware or persistence mechanisms. If confirmed malicious, the attacker could maintain exclusive control over a process, potentially leading to further exploitation or persistence within the environment.
data_source:
- Powershell Script Block Logging 4104
search: '`powershell` EventCode=4104 ScriptBlockText = "*Threading.Mutex*" | stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID | rename Computer as dest |rename UserID as user | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `powershell_creating_thread_mutex_filter`'
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.
references:
- 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/
drilldown_searches:
- name: View the detection results for - "$dest$" and "$user$"
  search: '%original_detection_search% | search  dest = "$dest$" user = "$user$"'
  earliest_offset: $info_min_time$
  latest_offset: $info_max_time$
- name: View risk events for the last 7 days for - "$dest$" and "$user$"
  search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$", "$user$") starthoursago=168  | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
  earliest_offset: $info_min_time$
  latest_offset: $info_max_time$
tags:
  analytic_story:
  - Malicious PowerShell
  asset_type: Endpoint
  confidence: 80
  impact: 50
  message: A suspicious powershell script contains Thread Mutex on host $dest$
  mitre_attack_id:
  - T1027
  - T1027.005
  - T1059.001
  observable:
  - name: dest
    type: Hostname
    role:
    - Victim
  - name: user
    type: User
    role:
    - Victim
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - EventCode
  - ScriptBlockText
  - Computer
  - UserID
  risk_score: 40
  security_domain: endpoint
tests:
- name: True Positive Test
  attack_data:
  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059.001/powershell_script_block_logging/sbl_xml.log
    source: XmlWinEventLog:Microsoft-Windows-PowerShell/Operational
    sourcetype: xmlwineventlog