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 file execution and network communication patterns indicative of a persistent, stealthy adversary. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced persistent threats before they cause significant damage to critical infrastructure.

YARA Rule

rule IMPLANT_4_v5 {
   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:
      $GEN_HASH = {0F BE C9 C1 C0 07 33 C1}
   condition:
      (uint16(0) == 0x5A4D or uint16(0) == 0xCFD0 or
      uint16(0) == 0xC3D4 or uint32(0) == 0x46445025 or
      uint32(1) == 0x6674725C) and all 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 1 string patterns in its detection logic.

References

False Positive Guidance

Scenario: Scheduled System Maintenance Task
Description: A legitimate scheduled task runs a script that uses mshta or powershell to execute maintenance scripts, which may resemble the implant’s behavior.
Filter/Exclusion: Exclude processes initiated by schtasks.exe or tasks with known maintenance names (e.g., Cleanup-System-Files).
Scenario: Admin PowerShell Script Execution
Description: An administrator runs a PowerShell script using powershell.exe to automate configuration changes, which may include obfuscated commands similar to the implant.
Filter/Exclusion: Exclude processes where the parent process is explorer.exe or cmd.exe and the script path is known internal admin script location (e.g., C:\Windows\System32\scripts\).
Scenario: Antivirus or EDR Tool Scan
Description: A security tool like Bitdefender or CrowdStrike performs a deep scan, triggering a script that uses mshta or powershell to analyze files, which may be flagged.
Filter/Exclusion: Exclude processes with parent process msiexec.exe or svchost.exe and where the command line includes known security tool paths.
Scenario: User-Initiated Software Installation
Description: A user installs a legitimate software package (e.g., Microsoft Office, Adobe Acrobat) that uses mshta or powershell for silent installation, triggering the rule.
Filter/Exclusion: Exclude processes where the command line includes known installers (e.g., setup.exe, msiexec.exe) or where the user is a non-administrator.
Scenario: Logon Script Execution
Description: A logon script runs a PowerShell or VBScript to configure user environment, which may include command-line arguments similar to the implant.