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.

Techniques

T1485

Sample rules

Common Ransomware Extensions

source: splunk
technicques:
- T1485

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.

Detection logic


| 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.action Filesystem.dest
        Filesystem.file_access_time Filesystem.file_create_time 
        Filesystem.file_hash Filesystem.file_modify_time
        Filesystem.file_name Filesystem.file_path 
        Filesystem.file_acl Filesystem.file_size
        Filesystem.process_guid Filesystem.process_id 
        Filesystem.user Filesystem.vendor_product

| `drop_dm_object_name(Filesystem)` 

| rex field=file_name "(?<file_extension>(\.[^\.]+){1,2})$"

| lookup update=true ransomware_extensions_lookup Extensions AS file_extension OUTPUT
Extensions Name 

| search Name !=False 

| stats min(firstTime) as firstTime 
        max(lastTime) as lastTime 
        dc(file_path) as path_count 
        dc(file_name) as file_count 
        values(action) as action 
        values(file_access_time) as file_access_time 
        values(file_create_time) as file_create_time 
        values(file_hash) as file_hash 
        values(file_modify_time) as file_modify_time
        values(file_acl) as file_acl 
        values(file_size) as file_size 
        values(process_guid) as process_guid 
        values(process_id) as process_id 
        values(user) as user 
        values(vendor_product) as vendor_product 
        values(file_name) as file_name 
        values(file_extension) as file_extension 
        values(Name) as Name 
  by dest 

| where path_count > 1 OR file_count > 20 

| `common_ransomware_extensions_filter`