ID | Technique | Tactic |
---|---|---|
T1485 | Data Destruction | Impact |
Detection: Windows High File Deletion Frequency
Description
The following analytic identifies a high frequency of file deletions by monitoring Sysmon EventCodes 23 and 26 for specific file extensions. This detection leverages Sysmon logs to track deleted target filenames, process names, and process IDs. Such activity is significant as it often indicates ransomware behavior, where files are encrypted and the originals are deleted. If confirmed malicious, this activity could lead to extensive data loss and operational disruption, as ransomware can render critical files inaccessible, demanding a ransom for their recovery.
Search
1`sysmon` EventCode IN ("23","26") TargetFilename IN ("*.cmd", "*.ini","*.gif", "*.jpg", "*.jpeg", "*.db", "*.ps1", "*.doc", "*.docx", "*.xls", "*.xlsx", "*.ppt", "*.pptx", "*.bmp","*.zip", "*.rar", "*.7z", "*.chm", "*.png", "*.log", "*.vbs", "*.js", "*.vhd", "*.bak", "*.wbcat", "*.bkf" , "*.backup*", "*.dsk", "*.win") NOT TargetFilename IN ("*\\INetCache\\Content.Outlook\\*")
2| stats count, values(TargetFilename) as deleted_files, min(_time) as firstTime, max(_time) as lastTime by user, dest, signature, signature_id, Image, process_name, process_guid
3| rename Image as process
4| where count >=100
5| `security_content_ctime(firstTime)`
6| `security_content_ctime(lastTime)`
7| `windows_high_file_deletion_frequency_filter`
Data Source
Name | Platform | Sourcetype | Source | Supported App |
---|---|---|---|---|
Sysmon EventID 23 | Windows | 'xmlwineventlog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
N/A |
Macros Used
Name | Value |
---|---|
security_content_ctime | convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$) |
windows_high_file_deletion_frequency_filter | search * |
windows_high_file_deletion_frequency_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
Implementation
To successfully implement this search, you need to ingest logs that include the deleted target file name, process name, and process ID from your endpoints. If you are using Sysmon, ensure you have at least version 2.0 of the Sysmon TA installed.
Known False Positives
Users may delete a large number of pictures or files in a folder, which could trigger this detection. Additionally, heavy usage of PowerBI and Outlook may also result in false positives.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
Elevated file deletion rate observed from process [$process_name$] on machine $dest$ | 72 | 90 | 80 |
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
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: 3