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Description

The following analytic detects the use of the PowerShell script block logging mechanism to detect the use of the Win32_ScheduledJob WMI class. This class allows the creation and management of scheduled tasks on Windows systems. However, due to security concerns, the class has been disabled by default in Windows systems, and its use must be explicitly enabled by modifying the registry. As a result, the detection of the use of this class may indicate malicious activity, especially if the class was enabled on the system by the attacker. Therefore, it is recommended to monitor the use of Win32_ScheduledJob through PowerShell script block logging and to investigate any suspicious activity.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2023-03-27
  • Author: Michael Haag, Splunk
  • ID: 47c69803-2c09-408b-b40a-063c064cbb16

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1059.001 PowerShell Execution
T1059 Command and Scripting Interpreter Execution
Kill Chain Phase
  • Installation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`powershell` EventCode=4104 ScriptBlockText="*win32_scheduledjob*" 
| 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)` 
| `windows_powershell_wmi_win32_scheduledjob_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_powershell_wmi_win32_scheduledjob_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • ScriptBlockText
  • dest
  • EventCode

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

False positives may be present based on legacy applications or utilities. Win32_ScheduledJob uses the Remote Procedure Call (RPC) protocol to create scheduled tasks on remote computers. It uses the DCOM (Distributed Component Object Model) infrastructure to establish a connection with the remote computer and invoke the necessary methods. The RPC service needs to be running on both the local and remote computers for the communication to take place.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
40.0 80 50 PowerShell attempting to create a task via WMI - Win32_ScheduledJob, was ran on $dest$.

:information_source: 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

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

source | version: 1