Ransomware Notes bulk creation

SPLUNK detection rule by Teoderick Contreras, Splunk · Apache-2.0

The following analytic identifies the bulk creation of ransomware notes (e.g., .txt, .html, .hta files) on an infected machine. It leverages Sysmon EventCode 11 to detect multiple instances of these file types being created within a short time frame. This activity is significant as it often indicates an active ransomware attack, where the attacker is notifying the victim of the encryption. If confirmed malicious, this behavior could lead to widespread data encryption, rendering critical files inaccessible and potentially causing significant operational disruption.

name: Ransomware Notes bulk creation
id: eff7919a-8330-11eb-83f8-acde48001122
version: 16
creation_date: '2021-03-19'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic identifies the bulk creation of ransomware notes (e.g., .txt, .html, .hta files) on an infected machine. It leverages Sysmon EventCode 11 to detect multiple instances of these file types being created within a short time frame. This activity is significant as it often indicates an active ransomware attack, where the attacker is notifying the victim of the encryption. If confirmed malicious, this behavior could lead to widespread data encryption, rendering critical files inaccessible and potentially causing significant operational disruption.
data_source:
    - Sysmon EventID 11
search: |-
    `sysmon` EventCode=11 file_name IN ("*\.txt","*\.html","*\.hta")
      | bin _time span=10s
      | stats min(_time) as firstTime max(_time) as lastTime dc(TargetFilename) as unique_readme_path_count values(TargetFilename) as list_of_readme_path 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_path) as file_path 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
        BY dest file_name
      | where unique_readme_path_count >= 15
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `ransomware_notes_bulk_creation_filter`
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.
known_false_positives: No false positives have been identified at this time.
references:
    - https://www.mandiant.com/resources/fin11-email-campaigns-precursor-for-ransomware-data-theft
    - https://blog.virustotal.com/2020/11/keep-your-friends-close-keep-ransomware.html
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 ("$dest$") | 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: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: A high frequency file creation of $file_name$ in different file path in host $dest$
analytic_story:
    - BlackMatter Ransomware
    - DarkSide Ransomware
    - Chaos Ransomware
    - Rhysida Ransomware
    - LockBit Ransomware
    - Medusa Ransomware
    - Black Basta Ransomware
    - Clop Ransomware
    - Cactus Ransomware
    - Termite Ransomware
    - Interlock Ransomware
    - NailaoLocker Ransomware
    - Hellcat Ransomware
asset_type: Endpoint
mitre_attack_id:
    - T1486
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/malware/clop/clop_a/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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221a3352-626f-405a-994d-0967fce5ee54

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