Detection: Windows File Without Extension In Critical Folder

Updated Date: 2024-09-30 ID: 0dbcac64-963c-11ec-bf04-acde48001122 Author: Teoderick Contreras, Bhavin Patel, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the creation of files without extensions in critical folders like "System32\Drivers." It leverages data from the Endpoint.Filesystem datamodel, focusing on file paths and creation times. This activity is significant as it may indicate the presence of destructive malware, such as HermeticWiper, which drops driver components in these directories. If confirmed malicious, this behavior could lead to severe system compromise, including boot sector wiping, resulting in potential data loss and system inoperability.

 1
 2| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*\\System32\\drivers\\*", "*\\syswow64\\drivers\\*") by _time span=5m Filesystem.dest Filesystem.user Filesystem.file_name Filesystem.file_path Filesystem.process_guid Filesystem.file_create_time 
 3| `drop_dm_object_name(Filesystem)` 
 4| rex field="file_name" "\.(?<extension>[^\.]*$)" 
 5| where isnull(extension) 
 6| join process_guid [
 7| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes by _time span=5m Processes.process_name Processes.dest Processes.process_guid Processes.user 
 8| `drop_dm_object_name(Processes)`] 
 9| stats count min(_time) as firstTime max(_time) as lastTime by dest process_name process_guid file_name file_path file_create_time user 
10| `security_content_ctime(firstTime)` 
11| `security_content_ctime(lastTime)` 
12| `windows_file_without_extension_in_critical_folder_filter`

Data Source

Name Platform Sourcetype Source
Sysmon EventID 1 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Sysmon EventID 11 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_file_without_extension_in_critical_folder_filter search *
windows_file_without_extension_in_critical_folder_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
T1485 Data Destruction Impact
KillChainPhase.ACTIONS_ON_OBJECTIVES
NistCategory.DE_CM
Cis18Value.CIS_10
APT38
LAPSUS$
Lazarus Group
Sandworm Team

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 Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

To successfully implement this search you need to be ingesting information on process that include the name of the Filesystem responsible for the changes from your endpoints into the Endpoint datamodel in the Filesystem node.

Known False Positives

Unknown at this point

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Driver file with out file extension drop in $file_path$ in $dest$ 90 90 100
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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: 3