Windows .Key File Creation in Root Directory

name: Windows .Key File Creation in Root Directory
id: 90e71722-8c0f-43b4-937a-6222325976c2
version: 2
creation_date: '2021-09-02'
modification_date: '2026-05-13'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: |-
    Detects the creation of a .key file in the root directory of the system drive.
    This activity was seen with various ransomware before performing encryption of files.
data_source:
    - Sysmon EventID 11
search: |-
    | tstats `security_content_summariesonly`
    count min(_time) as firstTime
          max(_time) as lastTime

    from datamodel=Endpoint.Filesystem where

    Filesystem.file_name="*.key"

    by Filesystem.dest Filesystem.file_create_time
       Filesystem.process_path Filesystem.process_guid
       Filesystem.process_id Filesystem.file_path
       Filesystem.action Filesystem.file_name
       Filesystem.user Filesystem.vendor_product

    | `drop_dm_object_name(Filesystem)`
    | where match(file_path, "^[A-Za-z]:\\\\[^\\\\]+\.key$")
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `windows__key_file_creation_in_root_directory_filter`
how_to_implement: The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
known_false_positives: False positives may occur if legitimate software or administrative tools create key files in the root directory, although this is uncommon in normal operations. Filter alerts based on known approved applications.
references:
    - https://www.cisa.gov/uscert/ncas/alerts/aa22-321a
drilldown_searches:
    - earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
      name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | 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: .key file created in the root of the system drive at $file_path$ on $dest$.
threat_objects:
    - field: file_path
      type: file_path
analytic_story:
    - 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/attack_techniques/T1022/snapattack/snapattack.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit