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.
- Type: Anomaly
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Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2024-05-18
- Author: Teoderick Contreras, Splunk, Steven Dick
- ID: 45b125c4-866f-11eb-a95a-acde48001122
Annotations
Kill Chain Phase
- Actions On Objectives
NIST
- DE.AE
CIS20
- CIS 10
CVE
Search
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`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\\*")
| 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
| rename Image as process
| 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:
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
- dest
- user
- Image
- ProcessID
- _time
How To Implement
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
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
72.0 | 90 | 80 | Elevated file deletion rate observed from process [$process_name$] on machine $dest$ |
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
source | version: 3