Detection: Linux Ingress Tool Transfer with Curl

Description

The following analytic detects the use of the curl command with specific switches (-O, -sO, -ksO, --output) commonly used to download remote scripts or binaries. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process names and command-line arguments. This activity is significant as it may indicate an attempt to download and execute potentially malicious files, often used in initial stages of an attack. If confirmed malicious, this could lead to unauthorized code execution, enabling attackers to compromise the system further.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name=curl by Processes.dest Processes.user Processes.parent_process_name Processes.process_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| where match(process, "(?i)(-O
 7|-sO
 8|-ksO
 9|--output)") 
10| `linux_ingress_tool_transfer_with_curl_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 1	Linux	'sysmon:linux'	'Syslog:Linux-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

False positives will be present. Tune and then change type to TTP.

Associated Analytic Story

• Ingress Tool Transfer

• Linux Living Off The Land

Risk Based Analytics (RBA)

References

• https://gtfobins.github.io/gtfobins/curl/

• https://curl.se/docs/manpage.html#-I

• https://gtfobins.github.io/gtfobins/curl/

• https://github.com/rapid7/metasploit-framework/search?q=curl

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: 4