BlackEnergy / Voodoo Bear Implant by APT28

Hunt Hypothesis

The hypothesis is that the detection rule identifies potential BlackEnergy / Voodoo Bear implant activity by APT28, characterized by suspicious process execution and network communication patterns indicative of command and control. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced persistent threat activity early in the attack lifecycle.

YARA Rule

rule IMPLANT_4_v4 {
   meta:
      description = "BlackEnergy / Voodoo Bear Implant by APT28"
      author = "US CERT"
      reference = "https://www.us-cert.gov/ncas/current-activity/2017/02/10/Enhanced-Analysis-GRIZZLY-STEPPE"
      date = "2017-02-10"
      score = 85
   strings:
      $DK_format1 = "/c format %c: /Y /Q" ascii
      $DK_format2 = "/c format %c: /Y /X /FS:NTFS" ascii
      $DK_physicaldrive = "PhysicalDrive%d" wide
      $DK_shutdown = "shutdown /r /t %d"
   condition:
      uint16(0) == 0x5A4D and all of ($DK*)
}

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 4 string patterns in its detection logic.

References

False Positive Guidance

Scenario: Scheduled System Maintenance Task
Description: A legitimate scheduled task runs a script that mimics the behavior of the BlackEnergy/Voodoo Bear implant, such as downloading files or modifying registry keys.
Filter/Exclusion: Exclude tasks associated with known system maintenance tools like schtasks.exe or Task Scheduler with names containing “Maintenance” or “Update”.
Scenario: Admin Performing Remote PowerShell Script Execution
Description: An administrator uses PowerShell to execute a script that resembles the implant’s behavior, such as establishing a reverse shell or downloading payloads.
Filter/Exclusion: Exclude PowerShell scripts executed by users with the “Administrators” group or those using the Invoke-Command cmdlet with a known admin tool like PsExec or PowerShell ISE.
Scenario: Antivirus Quarantine Process
Description: The endpoint security software quarantines a file that matches the implant’s signature, leading to false positive detection.
Filter/Exclusion: Exclude files flagged by the antivirus quarantine process, using a filter like file_hash or process_name matching the antivirus tool (e.g., Windows Defender, Bitdefender).
Scenario: Software Update or Patch Deployment
Description: A legitimate software update or patch deployment uses a method similar to the implant, such as downloading a payload or modifying system configurations.
Filter/Exclusion: Exclude processes initiated by known patch management tools like Microsoft Update, WSUS, or SCCM with specific command-line arguments.
Scenario: User-Initiated File Transfer via SMB
Description: A user transfers a file via SMB that matches the implant’s file signature, leading to false positive detection.
Filter/Exclusion: Exclude file transfers initiated by users with the “User” privilege level, or filter by SMB client tools