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Description

This analytic identifies excessive file deletion events in the Windows Defender folder. This technique was observed in the WhisperGate malware campaign, where adversaries exploited Nirsoft's advancedrun.exe to gain administrative privileges and then executed PowerShell commands to delete files within the Windows Defender application folder. Such behavior is a strong indicator that the offending process is attempting to corrupt a Windows Defender installation.

  • Type: TTP

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

  • Last Updated: 2024-03-05
  • Author: Teoderick Contreras, Splunk, Steven Dick
  • ID: b5baa09a-7a05-11ec-8da4-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1485 Data Destruction Impact
Kill Chain Phase
  • Actions On Objectives
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`sysmon` EventCode IN ("23","26") TargetFilename = "*\\ProgramData\\Microsoft\\Windows Defender\\*" 
| 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 >=50 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `excessive_file_deletion_in_windefender_folder_filter`

Macros

The SPL above uses the following Macros:

:information_source: excessive_file_deletion_in_windefender_folder_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.

  • _time
  • TargetFilename
  • user
  • dest
  • signature
  • signature_id
  • Image
  • process_name
  • process_path
  • process_guid

How To Implement

To successfully implement this search, you must ingest logs that include the process name, TargetFilename, and ProcessID executions from your endpoints. If you are utilizing Sysmon, ensure you have at least version 2.0 of the Sysmon TA installed.

Known False Positives

Windows Defender AV updates may trigger this alert. Please adjust the filter macros to mitigate false positives.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
25.0 50 50 Excessive file deletion events were detected in the Windows Defender folder on $dest$ by $user$. Investigate further to determine if this activity is malicious.

:information_source: 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

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: 2