Windows High File Deletion Frequency

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Description

This search looks for high frequency of file deletion relative to process name and process id. These events usually happen when the ransomware tries to encrypt the files with the ransomware file extensions and sysmon treat the original files to be deleted as soon it was replace as encrypted data.

• Type: Anomaly

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2023-04-14
• Author: Teoderick Contreras, Splunk
• ID: 45b125c4-866f-11eb-a95a-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1485	Data Destruction	Impact

Kill Chain Phase

• Actions On Objectives

NIST

• DE.AE

CIS20

• CIS 10

CVE

Search

`sysmon` EventCode=23 TargetFilename IN ("*.cmd", "*.ini","*.gif", "*.jpg", "*.jpeg", "*.db", "*.ps1", "*.doc*", "*.xls*", "*.ppt*", "*.bmp","*.zip", "*.rar", "*.7z", "*.chm", "*.png", "*.log", "*.vbs", "*.js", "*.vhd", "*.bak", "*.wbcat", "*.bkf" , "*.backup*", "*.dsk", "*.win") 
| stats values(TargetFilename) as deleted_files min(_time) as firstTime max(_time) as lastTime count by Computer user EventCode Image ProcessID 
|where count >=100 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_high_file_deletion_frequency_filter`

Macros

The SPL above uses the following Macros:

• sysmon
• security_content_ctime

windows_high_file_deletion_frequency_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

• EventCode
• TargetFilename
• Computer
• user
• Image
• ProcessID
• _time

How To Implement

To successfully implement this search, you need to be ingesting logs with the deleted target file name, process name and process id from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

user may delete bunch of pictures or files in a folder.

Associated Analytic Story

• Clop Ransomware
• DarkCrystal RAT
• Swift Slicer
• Data Destruction
• WhisperGate
• Sandworm Tools

RBA

Risk Score	Impact	Confidence	Message
72.0	90	80	High frequency file deletion activity detected on host $Computer$

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• 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
• https://www.microsoft.com/security/blog/2022/01/15/destructive-malware-targeting-ukrainian-organizations/

Test Dataset

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

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