This analytic will identify excessive file deletion events in the Windows Defender folder. This technique was seen in the WhisperGate malware campaign in which adversaries abused Nirsofts advancedrun.exe to gain administrative privilege to then execute PowerShell commands to delete files within the Windows Defender application folder. This behavior is a good indicator the offending process is trying to corrupt a Windows Defender installation.
- Type: TTP
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2022-01-20
- Author: Teoderick Contreras, Splunk
- ID: b5baa09a-7a05-11ec-8da4-acde48001122
Kill Chain Phase
- CIS 3
- CIS 5
- CIS 16
1 2 3 4 5 6 `sysmon` EventCode=23 TargetFilename = "*\\ProgramData\\Microsoft\\Windows Defender*" | stats values(TargetFilename) as deleted_files min(_time) as firstTime max(_time) as lastTime count by user EventCode Image ProcessID Computer |where count >=50 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `excessive_file_deletion_in_windefender_folder_filter`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
How To Implement
To successfully implement this search, you need to be ingesting logs with the process name, TargetFilename, and ProcessID executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.
Known False Positives
Windows Defender AV updates may cause this alert. Please update the filter macros to remove false positives.
Associated Analytic Story
|25.0||50||50||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.
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