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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.

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-11-10
  • Author: David Dorsey, Michael Haag, Splunk, Steven Dick
  • ID: a9e5c5db-db11-43ca-86a8-c852d1b2c0ec

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1485 Data Destruction Impact
Kill Chain Phase
  • Actions On Objectives
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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| 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`

Macros

The SPL above uses the following Macros:

:information_source: common_ransomware_extensions_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Filesystem.user
  • Filesystem.dest
  • Filesystem.file_path
  • Filesystem.file_name

How To Implement

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

RBA

Risk Score Impact Confidence Message
90.0 90 100 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.

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

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 | version: 5