WinEvent Scheduled Task Created to Spawn Shell

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Description

The following query utilizes Windows Security EventCode 4698, A scheduled task was created, to identify suspicious tasks registered on Windows either via schtasks.exe OR TaskService with a command to be executed with a native Windows shell (PowerShell, Cmd, Wscript, Cscript).\ The search will return the first time and last time the task was registered, as well as the Command to be executed, Task Name, Author, Enabled, and whether it is Hidden or not.\ schtasks.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64.\ The following DLL(s) are loaded when schtasks.exe or TaskService is launched -taskschd.dll. If found loaded by another process, it is possible a scheduled task is being registered within that process context in memory.\ Upon triage, identify the task scheduled source. Was it schtasks.exe or via TaskService? Review the job created and the Command to be executed. Capture any artifacts on disk and review. Identify any parallel processes within the same timeframe to identify source.

• Type: TTP

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

• Last Updated: 2023-04-05
• 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 
| xmlkv Message 
| search Command 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 dest, Task_Name, Command, Author, Enabled, Hidden 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `winevent_scheduled_task_created_to_spawn_shell_filter`

Macros

The SPL above uses the following Macros:

• wineventlog_security
• security_content_ctime

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

RBA

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

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

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