splunk_escuAnomaly

Ransomware Notes bulk creation

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.

MITRE ATT&CK

T1486

impact

Detection Query

`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`

Author

Teoderick Contreras, Splunk

Created

2026-04-15

Data Sources

Sysmon EventID 11

References

Tags

BlackMatter RansomwareDarkSide RansomwareChaos RansomwareRhysida RansomwareLockBit RansomwareMedusa RansomwareBlack Basta RansomwareClop RansomwareCactus RansomwareTermite RansomwareInterlock RansomwareNailaoLocker RansomwareHellcat Ransomware

Raw Content

name: Ransomware Notes bulk creation
id: eff7919a-8330-11eb-83f8-acde48001122
version: 15
date: '2026-04-15'
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"
rba:
    message: A high frequency file creation of $file_name$ in different file path in host $dest$
    risk_objects:
        - field: dest
          type: system
          score: 20
    threat_objects: []
tags:
    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
    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