Windows File Without Extension In Critical Folder

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

This analytic detects the creation of files without extensions in critical Windows system and driver-related directories, including but not limited to System32\Drivers, and other known Windows driver storage and loading paths. The analytic leverages telemetry from the Endpoint.Filesystem data model, with a focus on file creation events and file path analysis. File creation activity in these directories—particularly involving extensionless files—is highly suspicious, as it may indicate the presence of destructive or stealthy malware. This behavior is consistent with malware families such as HermeticWiper, which deploy kernel driver components into trusted Windows driver directories to obtain low-level access and execute destructive payloads. If confirmed malicious, this activity can result in severe system compromise, including the deployment of malicious drivers, boot-sector or filesystem destruction, and ultimately system inoperability and irreversible data loss.

name: Windows File Without Extension In Critical Folder
id: 0dbcac64-963c-11ec-bf04-acde48001122
version: 13
creation_date: '2022-02-25'
modification_date: '2026-07-27'
author: Teoderick Contreras, Bhavin Patel, Splunk
status: production
type: Anomaly
description: |-
    This analytic detects the creation of files without extensions in critical Windows system and driver-related directories, including but not limited to System32\Drivers, and other known Windows driver storage and loading paths.
    The analytic leverages telemetry from the Endpoint.Filesystem data model, with a focus on file creation events and file path analysis.
    File creation activity in these directories—particularly involving extensionless files—is highly suspicious, as it may indicate the presence of destructive or stealthy malware.
    This behavior is consistent with malware families such as HermeticWiper, which deploy kernel driver components into trusted Windows driver directories to obtain low-level access and execute destructive payloads.
    If confirmed malicious, this activity can result in severe system compromise, including the deployment of malicious drivers, boot-sector or filesystem destruction, and ultimately system inoperability and irreversible data loss.
data_source:
    - Sysmon EventID 11
search: |
    | tstats `security_content_summariesonly`
      count FROM datamodel=Endpoint.Filesystem where

    Filesystem.action IN ("created", "modified")
    Filesystem.file_path IN(
        "*:\\AMD\\*",
        "*:\\OEM\\*",
        "*:\\Windows\\Boot\\*",
        "*:\\Windows\\ELAMBKUP\\*",
        "*:\\Windows\\INF\\*",
        "*:\\Windows\\servicing\\*",
        "*:\\Windows\\System32\\Boot\\*",
        "*:\\Windows\\System32\\Drivers\\*",
        "*:\\Windows\\System32\\DriverStore\\*",
        "*:\\Windows\\System32\\Recovery\\*",
        "*:\\Windows\\SysWOW64\\Drivers\\*"
    )

    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" "\.(?<extension>[^\.]*$)"
    | where isnull(extension)
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `windows_file_without_extension_in_critical_folder_filter`
how_to_implement: To successfully implement this search you need to be ingesting information on process that include the name of the Filesystem responsible for the changes from your endpoints into the `Endpoint` datamodel in the `Filesystem` node.
known_false_positives: |-
    If you are leveraging Sysmon, you may see false positives related to folder creation, since Event ID 11 does not contain enough information to determine if the file is a File or a Directory. Filter out those entries when leveraging this analytic.
references:
    - https://blog.talosintelligence.com/2022/02/threat-advisory-hermeticwiper.html
    - https://www.splunk.com/en_us/blog/security/detecting-hermeticwiper.html
    - https://learn.microsoft.com/en-us/answers/questions/2184241/where-does-windows-installation-search-for-drivers
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") | 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: user
          type: user
          score: 20
          message: A file without extension [$file_name$] was dropped in a critical folder [$file_path$] by $user$
threat_objects:
    - field: file_name
      type: file_name
analytic_story:
    - Data Destruction
    - Hermetic Wiper
asset_type: Endpoint
mitre_attack_id:
    - T1485
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/hermetic_wiper/sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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