Detection: Windows Process Executed From Removable Media

Updated Date: 2025-01-17 ID: b483804a-4cc0-49a4-9f00-ac29ba844d08 Author: Steven Dick Type: Anomaly Product: Splunk Enterprise Security

Description

This analytic is used to identify when a removable media device is attached to a machine and then a process is executed from the same drive letter assigned to the removable media device. Adversaries and Insider Threats may use removable media devices for several malicious activities, including initial access, execution, and exfiltration.

 1
 2| tstats `security_content_summariesonly` count values(Processes.process) as process min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_current_directory=* AND NOT Processes.process_current_directory IN ("C:\\*","*\\sysvol\\*") by Processes.dest Processes.user Processes.process_name Processes.parent_process_name Processes.process_current_directory
 3
 4| `drop_dm_object_name(Processes)` 
 5
 6| rex field=process_current_directory "^(?<object_handle>[^\\\]+\\\)"
 7
 8| where isnotnull(object_handle)
 9
10| `security_content_ctime(firstTime)` 
11
12| `security_content_ctime(lastTime)`
13
14| join dest,object_handle
15  [
16| tstats `security_content_summariesonly` count from datamodel=Endpoint.Registry where Registry.registry_value_data="*:\\*" AND Registry.registry_path="*USBSTOR*" AND Registry.registry_path IN ("HKLM\\SOFTWARE\\Microsoft\\Windows Portable Devices\\Devices\\*","HKLM\\System\\CurrentControlSet\\Enum\\SWD\\WPDBUSENUM\\*") by Registry.dest,Registry.registry_value_data,Registry.registry_path
17   
18| `drop_dm_object_name(Registry)`
19   
20| eval object_handle = registry_value_data, object_name = replace(mvindex(split(mvindex(split(registry_path, "??"),1),"&amp;"),2),"PROD_","")
21  ]
22
23| `windows_process_executed_from_removable_media_filter`

Data Source

Name Platform Sourcetype Source
CrowdStrike ProcessRollup2 N/A 'crowdstrike:events:sensor' 'crowdstrike'
Sysmon EventID 1 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Sysmon EventID 12 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Sysmon EventID 13 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
windows_process_executed_from_removable_media_filter search *
windows_process_executed_from_removable_media_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1200 Hardware Additions Initial Access
T1025 Data from Removable Media Collection
T1091 Replication Through Removable Media Initial Access
Delivery
Exploitation
DE.AE
CIS 10

Default Configuration

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

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you must ingest endpoint logging that tracks changes to the HKLM\SOFTWARE\Microsoft\Windows Portable Devices\Devices\ or HKLM\System\CurrentControlSet\Enum\SWD\WPDBUSENUM\ registry keys as well as Process Execution commands. Ensure that the field from the event logs is being mapped to the proper fields in the Endpoint.Registry data model. This analytic joins the Process and Registry datamodels together based on the drive letter extract to the "object_handle" field from both datasets.

Known False Positives

Legitimate USB activity will also be detected. Please verify and investigate as appropriate.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The process [$process_name$] was launched using files on a removable storage device named [$object_name$] by [$user$] on $dest$

Risk Object Risk Object Type Risk Score Threat Objects
user user 35 object_handle, object_name, process_name
dest system 35 object_handle, object_name, process_name

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog

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: 1