Detection: Common Ransomware Extensions

Description

The following analytic detects modifications to files with extensions commonly associated with ransomware. It leverages the Endpoint.Filesystem data model to identify changes in file extensions that match known ransomware patterns. This activity is significant because it suggests an attacker is attempting to encrypt or alter files, potentially leading to severe data loss and operational disruption. If confirmed malicious, this activity could result in the encryption of critical data, rendering it inaccessible and causing significant damage to the organization's data integrity and availability.

Search

 1
 2| tstats `security_content_summariesonly` min(_time) as firstTime max(_time) as lastTime count latest(Filesystem.user) as user values(Filesystem.file_path) as file_path from datamodel=Endpoint.Filesystem by Filesystem.file_name Filesystem.dest _time span=1h 
 3| `drop_dm_object_name(Filesystem)` 
 4| rex field=file_name "(?<file_extension>\.[^\.]+)$" 
 5| rex field=file_path "(?<true_file_path>([^\\\]*\\\)*).*" 
 6| stats min(firstTime) as firstTime max(lastTime) as lastTime latest(user) as user dc(true_file_path) as path_count dc(file_name) as file_count latest(file_name) as file_name latest(true_file_path) as file_path by dest file_extension 
 7| `security_content_ctime(lastTime)` 
 8| `security_content_ctime(firstTime)` 
 9| `ransomware_extensions` 
10| where path_count > 1 OR file_count > 20 
11| `common_ransomware_extensions_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

You must be ingesting data that records the filesystem activity from your hosts to populate the Endpoint Filesystem data model node. To see the additional metadata, add the following fields, if not already present, please review the detailed documentation on how to create a new field within Incident Review may be found here: https://docs.splunk.com/Documentation/ES/5.3.0/Admin/Customizenotables#Add_a_field_to_the_notable_event_details

Known False Positives

It is possible for a legitimate file with these extensions to be created. If this is a true ransomware attack, there will be a large number of files created with these extensions.

Associated Analytic Story

• Clop Ransomware

• LockBit Ransomware

• Prestige Ransomware

• Ransomware

• Rhysida Ransomware

• Ryuk Ransomware

• SamSam Ransomware

Risk Based Analytics (RBA)

References

• https://github.com/splunk/security_content/issues/2448

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