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)
 3as lastTime from datamodel=Endpoint.Processes where 
 4`process_curl` 
 5Processes.process IN ("*-O *","*--output*") 
 6Processes.process IN (
 7      "*:\\PerfLogs\\*",
 8      "*:\\Windows\\Temp\\*",
 9      "*\\AppData\\*",
10      "*\\ProgramData\\*",
11      "*\\Users\\Public\\*",
12      "*%AppData%*",
13      "*%Public%*",
14      "*%Temp%*",
15      "*%tmp%*"
16      )
17by Processes.action Processes.dest Processes.original_file_name Processes.parent_process
18   Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id
19   Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec
20   Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level
21   Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
22
23| `drop_dm_object_name(Processes)` 
24
25| `security_content_ctime(firstTime)` 
26
27| `security_content_ctime(lastTime)`
28
29| `windows_curl_download_to_suspicious_path_filter`

Data Source

Name	Platform	Sourcetype	Source
Cisco Network Visibility Module Flow Data	Network	'cisco:nvm:flowdata'	'not_applicable'
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

• Black Basta Ransomware

• China-Nexus Threat Activity

• Cisco Network Visibility Module Analytics

• Compromised Windows Host

• Forest Blizzard

• IcedID

• Ingress Tool Transfer

• Salt Typhoon

Risk Based Analytics (RBA)

Risk Message:

An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ to download a file to a suspicious directory.

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: 14