Detection: Windows File Without Extension In Critical Folder

Description

This analytic detects the creation of files without extensions in critical Windows system and driver-related directories, including but not limited to System32\Drivers, Windows\WinSxS, and other known Windows driver storage and loading paths. The detection has been expanded to comprehensively cover all commonly abused and legitimate Windows driver folder locations, increasing visibility into attempts to stage or deploy kernel-mode components. The analytic leverages telemetry from the Endpoint.Filesystem data model, with a focus on file creation events and file path analysis. File creation activity in these directories—particularly involving extensionless files—is highly suspicious, as it may indicate the presence of destructive or stealthy malware. This behavior is consistent with malware families such as HermeticWiper, which deploy kernel driver components into trusted Windows driver directories to obtain low-level access and execute destructive payloads. If confirmed malicious, this activity can result in severe system compromise, including the deployment of malicious drivers, boot-sector or filesystem destruction, and ultimately system inoperability and irreversible data loss.

Search

 1
 2| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Filesystem
 3where Filesystem.file_path IN("*\\System32\\drivers\\*", "*\\syswow64\\drivers\\*", "*\\WINDOWS\\inf\\*","*\\Program Files*", "*\\WINDOWS\\System32\\DriverStore\\*","*:\\Windows\\WinSxS\\*","*\\ProgramData\\Microsoft\\Windows Defender\\Definition Updates\\*","*\\ProgramData\\Microsoft\\Windows Defender\\Platform\\*","*\\Windows\\servicing\\*", "*\\Windows\\ELAMBKUP\\*","*\\Windows\\Boot\\*","*\\System32\\Boot\\*","*\\System32\\Recovery\\*", "C:\\AMD\\*", "C:\\OEM\\*")
 4by Filesystem.action Filesystem.dest Filesystem.file_access_time Filesystem.file_create_time
 5Filesystem.file_hash Filesystem.file_modify_time Filesystem.file_name Filesystem.file_path
 6Filesystem.file_acl Filesystem.file_size Filesystem.process_guid Filesystem.process_id
 7Filesystem.user Filesystem.vendor_product 
 8
 9| `drop_dm_object_name(Filesystem)` 
10
11| rex field="file_name" "\.(?<extension>[^\.]*$)" 
12
13| where isnull(extension) 
14
15| `security_content_ctime(firstTime)`
16
17| `security_content_ctime(lastTime)` 
18
19| `windows_file_without_extension_in_critical_folder_filter`

Data Source

Name	Platform	Sourcetype	Source
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

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

• Data Destruction

• Hermetic Wiper

Risk Based Analytics (RBA)

Risk Message:

Driver file with out file extension drop in $file_path$ on $dest$

References

• https://blog.talosintelligence.com/2022/02/threat-advisory-hermeticwiper.html

• https://www.splunk.com/en_us/blog/security/detecting-hermeticwiper.html

• https://learn.microsoft.com/en-us/answers/questions/2184241/where-does-windows-installation-search-for-drivers

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: 7