Detection: Windows Scheduled Task Service Spawned Shell

Description

The following analytic detects when the Task Scheduler service ("svchost.exe -k netsvcs -p -s Schedule") spawns common command line, scripting, or shell execution binaries such as "powershell.exe" or "cmd.exe". This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process and parent process relationships. This activity is significant as attackers often abuse the Task Scheduler for execution and persistence, blending in with legitimate Windows operations. If confirmed malicious, this could allow attackers to execute arbitrary code, maintain persistence, or escalate privileges within the environment.

Search

 1
 2| tstats `security_content_summariesonly`
 3count min(_time) as firstTime
 4      max(_time) as lastTime
 5
 6from datamodel=Endpoint.Processes where
 7
 8Processes.parent_process_name="svchost.exe"
 9Processes.parent_process="*-k*"
10Processes.parent_process= "*netsvcs*"
11Processes.parent_process="*-p*"
12Processes.parent_process="*-s*"
13Processes.parent_process="*Schedule*"
14Processes.process_name IN(
15    "bash.exe",
16    "cmd.exe",
17    "cscript.exe",
18    "ksh.exe",
19    "powershell.exe",
20    "pwsh.exe",
21    "scrcons.exe",
22    "sh.exe",
23    "wscript.exe",
24    "zsh.exe"
25)
26
27by Processes.action Processes.dest Processes.original_file_name
28   Processes.parent_process Processes.parent_process_exec
29   Processes.parent_process_guid Processes.parent_process_id
30   Processes.parent_process_name Processes.parent_process_path
31   Processes.process Processes.process_exec Processes.process_guid
32   Processes.process_hash Processes.process_id Processes.process_integrity_level
33   Processes.process_name Processes.process_path Processes.user
34   Processes.user_id Processes.vendor_product
35
36
37| `drop_dm_object_name(Processes)`
38
39| `security_content_ctime(firstTime)`
40
41| `security_content_ctime(lastTime)`
42
43| `windows_scheduled_task_service_spawned_shell_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	Other	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Certain scheduled tasks will intentionally call a script via PowerShell or Cmd for example. These will trigger this detection. Evaluate if they are legitimate and apply filters as needed.

Associated Analytic Story

• Windows Persistence Techniques

Risk Based Analytics (RBA)

Risk Message:

A windows scheduled task spawned the shell application $process_name$ on $dest$.

References

• https://www.mandiant.com/resources/blog/tracking-evolution-gootloader-operations

• https://nasbench.medium.com/a-deep-dive-into-windows-scheduled-tasks-and-the-processes-running-them-218d1eed4cce

• https://attack.mitre.org/techniques/T1053/005/

Detection Testing

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: GitHub | Version: 10