LoFP / 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 Searches for file modifications that commonly occur with Ransomware to detect modifications to files with extensions that are commonly used by Ransomware. The detection is made by searches for changes in the datamodel=Endpoint.Filesystem, specifically modifications to file extensions that match those commonly used by Ransomware. The detection is important because it suggests that an attacker is attempting to encrypt or otherwise modify files in the environment using malware, potentially leading to data loss that can cause significant damage to an organization’s data and systems. False positives might occur so the SOC must investigate the affected system to determine the source of the modification and take appropriate action to contain and remediate the attack.

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.file_name Filesystem.dest _time span=1h 
| `drop_dm_object_name(Filesystem)` 
| rex field=file_name "(?<file_extension>\.[^\.]+)$" 
| rex field=file_path "(?<true_file_path>([^\\\]*\\\)*).*" 
| 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 
| `security_content_ctime(lastTime)` 
| `security_content_ctime(firstTime)` 
| `ransomware_extensions` 
| where path_count > 1 OR file_count > 20 
| `common_ransomware_extensions_filter`