User Discovery With Env Vars PowerShell Script Block

name: User Discovery With Env Vars PowerShell Script Block
id: 77f41d9e-b8be-47e3-ab35-5776f5ec1d20
version: 10
creation_date: '2021-08-24'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: Hunting
description: The following analytic detects the use of PowerShell environment variables to identify the current logged user by leveraging PowerShell Script Block Logging (EventCode=4104). This method monitors script blocks containing `$env:UserName` or `[System.Environment]::UserName`. Identifying this activity is significant as adversaries and Red Teams may use it for situational awareness and Active Directory discovery on compromised endpoints. If confirmed malicious, this activity could allow attackers to gain insights into user context, aiding in further exploitation and lateral movement within the network.
data_source:
    - Powershell Script Block Logging 4104
search: |-
    `powershell` EventCode=4104 (ScriptBlockText = "*$env:UserName*" OR ScriptBlockText = "*[System.Environment]::UserName*")
      | fillnull
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY dest signature signature_id
           user_id vendor_product EventID
           Guid Opcode Name
           Path ProcessID ScriptBlockId
           ScriptBlockText
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `user_discovery_with_env_vars_powershell_script_block_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://help.splunk.com/en/security-offerings/splunk-user-behavior-analytics/get-data-in/5.4.1/add-other-data-to-splunk-uba/configure-powershell-logging-to-see-powershell-anomalies-in-splunk-uba.
known_false_positives: Administrators or power users may use this PowerShell commandlet for troubleshooting.
references:
    - https://attack.mitre.org/techniques/T1033/
analytic_story:
    - Active Directory Discovery
asset_type: Endpoint
mitre_attack_id:
    - T1033
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1033/AD_discovery/windows-powershell-xml.log
          source: XmlWinEventLog:Microsoft-Windows-PowerShell/Operational
          sourcetype: XmlWinEventLog
      test_type: unit