Detection: Windows Curl Download to Suspicious Path

Description

The following analytic detects the use of Windows Curl.exe to download a file to a suspicious location, such as AppData, ProgramData, or Public directories. It leverages data from Endpoint Detection and Response (EDR) agents, focusing on command-line executions that include the -O or --output options. This activity is significant because downloading files to these locations can indicate an attempt to bypass security controls or establish persistence. If confirmed malicious, this behavior could lead to unauthorized code execution, data exfiltration, or further compromise of the system.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_curl` Processes.process IN ("*-O *","*--output*") Processes.process IN ("*\\appdata\\*","*\\programdata\\*","*\\public\\*") by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.original_file_name Processes.process Processes.process_id Processes.parent_process_id 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `windows_curl_download_to_suspicious_path_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	N/A	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Windows Event Log Security 4688	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'

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

It is possible Administrators or super users will use Curl for legitimate purposes. Filter as needed.

Associated Analytic Story

• Compromised Windows Host

• Forest Blizzard

• IcedID

• Ingress Tool Transfer

Risk Based Analytics (RBA)

References

• https://thedfirreport.com/2021/10/18/icedid-to-xinglocker-ransomware-in-24-hours/

• https://attack.mitre.org/techniques/T1105/

• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1105/T1105.md

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: 5