GitHub Repo

Detection: Windows .Key File Creation in Root Directory

Updated Date: 2026-04-13 ID: 90e71722-8c0f-43b4-937a-6222325976c2 Author: Raven Tait, Splunk Type: Anomaly Product: Splunk Enterprise Security

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.

 1
 2| tstats `security_content_summariesonly`
 3count min(_time) as firstTime
 4      max(_time) as lastTime
 5
 6from datamodel=Endpoint.Filesystem where
 7
 8Filesystem.file_name="*.key"
 9
10by Filesystem.dest Filesystem.file_create_time
11   Filesystem.process_path Filesystem.process_guid
12   Filesystem.process_id Filesystem.file_path
13   Filesystem.action Filesystem.file_name
14   Filesystem.user Filesystem.vendor_product
15
16
17| `drop_dm_object_name(Filesystem)`
18
19| where match(file_path, "^[A-Za-z]:\\\\[^\\\\]+\.key$")
20
21| `security_content_ctime(firstTime)`
22
23| `security_content_ctime(lastTime)`
24
25| `windows__key_file_creation_in_root_directory_filter`

Data Source

Name Platform Sourcetype Source
Sysmon EventID 11 Windows icon Windows 'XmlWinEventLog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
windows__key_file_creation_in_root_directory_filter search *
windows__key_file_creation_in_root_directory_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1486 Data Encrypted for Impact Impact
Actions on Objectives
DE.AE
CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

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.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

.key file created in the root of the system drive at $file_path$ on $dest$.

Risk Object Risk Object Type Risk Score Threat Objects
dest system 20 file_path

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1