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Description

This detection detects a high amount of file deletions in a short time for specific file types. This can be an indicator for a malicious insider.

  • Type: Anomaly
  • Product: Splunk Behavioral Analytics
  • Datamodel: Endpoint_Filesystem
  • Last Updated: 2021-12-07
  • Author: Patrick Bareiss, Splunk
  • ID: b6200efd-13bd-4336-920a-057b25bbcfaf

ATT&CK

ID Technique Tactic
T1485 Data Destruction Impact
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| from read_ssa_enriched_events() 
| eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)) 
| eval action=ucast(map_get(input_event, "action"), "string", null), process=ucast(map_get(input_event, "process"), "string", null), file_name=ucast(map_get(input_event, "file_name"), "string", null), file_path=ucast(map_get(input_event, "file_path"), "string", null), dest_user_id=ucast(map_get(input_event, "dest_user_id"), "string", null), dest_device_id=ucast(map_get(input_event, "dest_device_id"), "string", null) 
| where "Endpoint_Filesystem" IN(_datamodels) 
| where action="deleted" 
| where like(file_name, "%.cmd") OR like(file_name, "%.ini") OR like(file_name, "%.gif") OR like(file_name, "%.jpg") OR like(file_name, "%.jpeg") OR like(file_name, "%.db") OR like(file_name, "%.doc%") OR like(file_name, "%.ps1") OR like(file_name, "%.xls%") OR like(file_name, "%.ppt%") OR like(file_name, "%.bmp") OR like(file_name, "%.zip") OR like(file_name, "%.rar") OR like(file_name, "%.7z") OR like(file_name, "%.chm") OR like(file_name, "%.png") OR like(file_name, "%.log") OR like(file_name, "%.vbs") OR like(file_name, "%.js") 
| stats count(file_name) AS count BY dest_user_id, dest_device_id, span(timestamp, 10m) 
| where count > 20 
| eval start_time=window_start, end_time=window_end, entities=mvappend(dest_user_id, dest_device_id), body=create_map(["count", count]) 
| into write_ssa_detected_events();

Macros

The SPL above uses the following Macros:

Note that 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 field

  • action
  • process
  • file_name
  • file_path

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Filesytem node.

Known False Positives

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

Associated Analytic story

Kill Chain Phase

  • Exploitation

RBA

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

Note that risk score is calculated base on the following formula: (Impact * Confidence)/100

Reference

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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