WinEvent Scheduled Task Created to Spawn Shell

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Description

The following analytic detects the creation of scheduled tasks designed to execute commands using native Windows shells like PowerShell, Cmd, Wscript, or Cscript. It leverages Windows Security EventCode 4698 to identify when such tasks are registered. This activity is significant as it may indicate an attempt to establish persistence or execute malicious commands on a system. If confirmed malicious, this could allow an attacker to maintain access, execute arbitrary code, or escalate privileges, posing a severe threat to the environment.

• Type: TTP

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

• Last Updated: 2024-05-18
• Author: Michael Haag, Splunk
• ID: 203ef0ea-9bd8-11eb-8201-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1053.005	Scheduled Task	Execution, Persistence, Privilege Escalation

T1053

Scheduled Task/Job

Execution, Persistence, Privilege Escalation

Kill Chain Phase

• Installation
• Exploitation

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

`wineventlog_security` EventCode=4698 TaskContent IN ("*powershell.exe*", "*wscript.exe*", "*cscript.exe*", "*cmd.exe*", "*sh.exe*", "*ksh.exe*", "*zsh.exe*", "*bash.exe*", "*scrcons.exe*", "*pwsh.exe*") 
| stats count min(_time) as firstTime max(_time) as lastTime by Computer, TaskName, TaskContent 
| rename Computer as dest 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `winevent_scheduled_task_created_to_spawn_shell_filter`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• wineventlog_security

winevent_scheduled_task_created_to_spawn_shell_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
• dest
• Task_Name
• Description
• Command

How To Implement

To successfully implement this search, you need to be ingesting Windows Security Event Logs with 4698 EventCode enabled. The Windows TA is also required.

Known False Positives

False positives are possible if legitimate applications are allowed to register tasks that call a shell to be spawned. Filter as needed based on command-line or processes that are used legitimately.

Associated Analytic Story

• Ransomware
• Windows Persistence Techniques
• Winter Vivern
• Ryuk Ransomware
• CISA AA22-257A
• Scheduled Tasks
• Windows Error Reporting Service Elevation of Privilege Vulnerability

RBA

Risk Score	Impact	Confidence	Message
70.0	70	100	A windows scheduled task was created (task name=$TaskName$) on $dest$ by the following command: $TaskContent$

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://research.checkpoint.com/2021/irans-apt34-returns-with-an-updated-arsenal/
• https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventID=4698
• https://redcanary.com/threat-detection-report/techniques/scheduled-task-job/
• https://docs.microsoft.com/en-us/windows/win32/taskschd/time-trigger-example–scripting-?redirectedfrom=MSDN

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: 4