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` 
 3  min(_time) as firstTime 
 4  max(_time) as lastTime 
 5  count latest(Filesystem.user) as user 
 6        values(Filesystem.file_path) as file_path 
 7  from datamodel=Endpoint.Filesystem by 
 8        Filesystem.action Filesystem.dest
 9        Filesystem.file_access_time Filesystem.file_create_time 
10        Filesystem.file_hash Filesystem.file_modify_time
11        Filesystem.file_name Filesystem.file_path 
12        Filesystem.file_acl Filesystem.file_size
13        Filesystem.process_guid Filesystem.process_id 
14        Filesystem.user Filesystem.vendor_product
15
16| `drop_dm_object_name(Filesystem)` 
17
18| rex field=file_name "(?<file_extension>(\.[^\.]+){1,2})$"
19
20| lookup update=true ransomware_extensions_lookup Extensions AS file_extension OUTPUT
21Extensions Name 
22
23| search Name !=False 
24
25| stats min(firstTime) as firstTime 
26        max(lastTime) as lastTime 
27        dc(file_path) as path_count 
28        dc(file_name) as file_count 
29        values(action) as action 
30        values(file_access_time) as file_access_time 
31        values(file_create_time) as file_create_time 
32        values(file_hash) as file_hash 
33        values(file_modify_time) as file_modify_time
34        values(file_acl) as file_acl 
35        values(file_size) as file_size 
36        values(process_guid) as process_guid 
37        values(process_id) as process_id 
38        values(user) as user 
39        values(vendor_product) as vendor_product 
40        values(file_name) as file_name 
41        values(file_extension) as file_extension 
42        values(Name) as Name 
43  by dest 
44
45| where path_count > 1 OR file_count > 20 
46
47| `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

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

• Black Basta Ransomware

• Clop Ransomware

• Interlock Ransomware

• LockBit Ransomware

• Medusa Ransomware

• NailaoLocker Ransomware

• Prestige Ransomware

• Ransomware

• Rhysida Ransomware

• Ryuk Ransomware

• SamSam Ransomware

• Termite Ransomware

Risk Based Analytics (RBA)

Risk Message:

The device $dest$ wrote $file_count$ files to $path_count$ path(s) with the $file_extension$ extension. This extension and behavior may indicate a $Name$ ransomware attack.

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: 16