Detection: Process Creating LNK file in Suspicious Location

Description

The following analytic detects a process creating a .lnk file in suspicious locations such as C:\User* or *\Local\Temp\*. It leverages filesystem and process activity data from the Endpoint data model to identify this behavior. This activity is significant because creating .lnk files in these directories is a common tactic used by spear phishing tools to establish persistence or execute malicious payloads. If confirmed malicious, this could allow an attacker to maintain persistence, execute arbitrary code, or further compromise the system.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_name="*.lnk" AND (Filesystem.file_path="C:\\Users\\*" OR Filesystem.file_path="*\\Temp\\*") by _time span=1h Filesystem.process_guid Filesystem.file_name Filesystem.file_path Filesystem.file_hash Filesystem.user 
 3| `drop_dm_object_name(Filesystem)` 
 4| rename process_guid as lnk_guid 
 5| join lnk_guid _time [
 6| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_name=* by _time span=1h Processes.parent_process_name Processes.parent_process_guid Processes.process_name Processes.dest Processes.process Processes.path 
 7| `drop_dm_object_name(Processes)` 
 8| rename parent_process_guid as lnk_guid] 
 9| `security_content_ctime(firstTime)` 
10| `security_content_ctime(lastTime)` 
11| table firstTime, lastTime, lnk_guid, user, dest, file_name, file_path, process_name, process, process_path, file_hash 
12| `process_creating_lnk_file_in_suspicious_location_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 1	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Sysmon EventID 11	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

You must be ingesting data that records filesystem and process activity from your hosts to populate the Endpoint data model. This is typically populated via endpoint detection-and-response product, such as Carbon Black, or endpoint data sources, such as Sysmon.

Known False Positives

This detection should yield little or no false positive results. It is uncommon for LNK files to be executed from temporary or user directories.

Associated Analytic Story

• Amadey

• Gozi Malware

• IcedID

• Qakbot

• Spearphishing Attachments

Risk Based Analytics (RBA)

References

• https://attack.mitre.org/techniques/T1566/001/

• https://www.trendmicro.com/en_us/research/17/e/rising-trend-attackers-using-lnk-files-download-malware.html

• https://twitter.com/pr0xylife/status/1590394227758104576

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: 8