Detects VBS Agent from BlackEnergy Report - file Dropbearrun.vbs

Hunt Hypothesis

The detection of the Dropbearrun.vbs file indicates potential deployment of a VBS-based agent associated with the BlackEnergy malware family. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify early-stage compromises and prevent lateral movement within the network.

YARA Rule

rule BlackEnergy_VBS_Agent 
{

    meta:
        description = "Detects VBS Agent from BlackEnergy Report - file Dropbearrun.vbs"
        author = "Florian Roth"
        reference = "http://feedproxy.google.com/~r/eset/blog/~3/BXJbnGSvEFc/"
        date = "2016-01-03"
        hash = "b90f268b5e7f70af1687d9825c09df15908ad3a6978b328dc88f96143a64af0f"
    
    strings:
        $s0 = "WshShell.Run \"dropbear.exe -r rsa -d dss -a -p 6789\", 0, false" fullword ascii
        $s1 = "WshShell.CurrentDirectory = \"C:\\WINDOWS\\TEMP\\Dropbear\\\"" fullword ascii
        $s2 = "Set WshShell = CreateObject(\"WScript.Shell\")" fullword ascii /* Goodware String - occured 1 times */
   
    condition:
        filesize < 1KB and 2 of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 3 string patterns in its detection logic.

References

• http://feedproxy.google.com/~r/eset/blog/~3/BXJbnGSvEFc/
• Source Rule

False Positive Guidance

• Scenario: System administrator deploys a scheduled job using Task Scheduler to run a VBScript named Dropbearrun.vbs for routine system maintenance.
  Filter/Exclusion: Check for presence of Task Scheduler in the process tree or filter by CommandLine containing schtasks or schtasks.exe.

• Scenario: A Windows Update or Microsoft Endpoint Manager (MEM) deployment includes a VBScript file named Dropbearrun.vbs as part of a legitimate patching process.
  Filter/Exclusion: Filter by ProcessName containing wuauclt.exe or setup.exe, or check for presence of Microsoft Endpoint Manager in the process tree.

• Scenario: A third-party backup tool (e.g., Veeam Backup & Replication) generates a temporary VBScript file named Dropbearrun.vbs during a backup operation.
  Filter/Exclusion: Filter by ProcessName containing veeam.exe or check for presence of Veeam Backup & Replication in the process tree.

• Scenario: A system diagnostic tool (e.g., Windows Performance Analyzer or Sysinternals tools) uses a VBScript file named Dropbearrun.vbs for log parsing or data collection.
  Filter/Exclusion: Filter by ProcessName containing perfmon.exe, taskmgr.exe, or ProcessMonitor.exe, or check for presence of Sysinternals in the process tree.

• Scenario: An IT automation script (e.g., PowerShell script or Batch file) generates a VBScript named Dropbearrun.vbs dynamically for configuration management tasks.
  Filter/Exclusion: Filter by ProcessName containing powershell.exe or cmd.exe, and check for