Try in Splunk Security Cloud

Description

The search looks for file modifications with extensions commonly used by Ransomware

  • Type: Hunting
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2020-11-09
  • Author: David Dorsey, Splunk
  • 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
  • PR.PT
  • DE.CM
CIS20
  • CIS 8
CVE 


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| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime values(Filesystem.user) as user values(Filesystem.dest) as dest values(Filesystem.file_path) as file_path from datamodel=Endpoint.Filesystem by Filesystem.file_name 
| `drop_dm_object_name(Filesystem)` 
| `security_content_ctime(lastTime)` 
| `security_content_ctime(firstTime)`
| rex field=file_name "(?<file_extension>\.[^\.]+)$" 
| `ransomware_extensions` 
| `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 file-system data model node. If you are using Sysmon, you will need a Splunk Universal Forwarder on each endpoint from which you want to collect data.
This search produces fields (query,query_length,count) that are not yet supported by ES Incident Review and therefore cannot be viewed when a notable event is raised. These fields contribute additional context to the notable. To see the additional metadata, add the following fields, if not already present, to Incident Review - Event Attributes (Configure > Incident Management > Incident Review Settings > Add New Entry):\n1. Label: Name, Field: Name\

  1. \
  2. Label: File Extension, Field: file_extension
    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 A file - $file_name$ was written to disk on endpoint $dest$ by user $user$, this is indicative of a known ransomware file extension and should be reviewed immediately.

: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: 4