Common Ransomware Extensions

name: Common Ransomware Extensions
id: a9e5c5db-db11-43ca-86a8-c852d1b2c0ec
version: 19
date: '2026-03-10'
author: David Dorsey, Michael Haag, Splunk, Steven Dick
status: production
type: TTP
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.
data_source:
    - Sysmon EventID 11
search: |
    | 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
      where NOT Filesystem.file_name IN (
        "*.bat",
        "*.cmd",
        "*.com",
        "*.cpl",
        "*.dll",
        "*.doc",
        "*.docx",
        "*.exe",
        "*.gif",
        "*.jar",
        "*.jpeg",
        "*.jpg",
        "*.js",
        "*.lnk",
        "*.pif",
        "*.png",
        "*.ppt",
        "*.pptx",
        "*.ps1",
        "*.psm1",
        "*.scr",
        "*.sys",
        "*.txt",
        "*.vbs",
        "*.wsf",
        "*.xls",
        "*.xlsx"
      )
      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})$"
    | lookup update=true ransomware_extensions_lookup Extensions AS file_extension OUTPUT Extensions Name
    | search Name !=False
    | stats min(firstTime) as firstTime
            max(lastTime) as lastTime
            dc(file_path) as path_count
            dc(file_name) as file_count
            values(action) as action
            values(file_access_time) as file_access_time
            values(file_create_time) as file_create_time
            values(file_hash) as file_hash
            values(file_modify_time) as file_modify_time
            values(file_acl) as file_acl
            values(file_size) as file_size
            values(file_path) as file_path
            values(process_guid) as process_guid
            values(process_id) as process_id
            values(user) as user
            values(vendor_product) as vendor_product
            values(file_name) as file_name
            values(file_extension) as file_extension
            values(Name) as Name
      by dest
    | where path_count > 1 OR file_count > 20
    | `common_ransomware_extensions_filter`
how_to_implement: You must be ingesting data that records the filesystem activity from your hosts to populate the Endpoint Filesystem data model node. To see the additional metadata, add the following fields, if not already present, please review the detailed documentation on how to create a new field within Mission Control Queue
known_false_positives: It is possible for a legitimate file with these extensions to be created. If this is a true ransomware attack, there will be a large number of files created with these extensions.
references:
    - https://github.com/splunk/security_content/issues/2448
drilldown_searches:
    - name: View the detection results for "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") starthoursago=168 | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
rba:
    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.
    risk_objects:
        - field: user
          type: user
          score: 50
        - field: dest
          type: system
          score: 50
    threat_objects: []
tags:
    analytic_story:
        - Rhysida Ransomware
        - Prestige Ransomware
        - Ransomware
        - LockBit Ransomware
        - Medusa Ransomware
        - SamSam Ransomware
        - Clop Ransomware
        - Ryuk Ransomware
        - Black Basta Ransomware
        - Termite Ransomware
        - Interlock Ransomware
        - NailaoLocker Ransomware
    asset_type: Endpoint
    mitre_attack_id:
        - T1485
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1485/ransomware_notes/ransom-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog