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 commonly associated with this advanced persistent threat. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect early-stage compromise and prevent lateral movement and data exfiltration by state-sponsored adversaries.

YARA Rule

rule IMPLANT_4_v3_AlternativeRule {
   meta:
      description = "BlackEnergy / Voodoo Bear Implant by APT28"
      comment = "Alternative rule - not based on the original samples but samples on which the original rule matched"
      author = "Florian Roth"
      reference = "US CERT Grizzly Steppe Report"
      date = "2017-02-12"
      hash1 = "2244fe9c5d038edcb5406b45361613cf3909c491e47debef35329060b00c985a"
   strings:
      $op1 = { 33 c9 41 ff 13 13 c9 ff 13 72 f8 c3 53 1e 01 00 } /* Opcode */
      $op2 = { 21 da 40 00 00 a0 40 00 08 a0 40 00 b0 70 40 00 } /* Opcode */
   condition:
      ( uint16(0) == 0x5a4d 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 2 string patterns in its detection logic.

References

• US CERT Grizzly Steppe Report
• Source Rule

False Positive Guidance

• Scenario: Legitimate scheduled system cleanup task using cleanmgr.exe
  Description: A scheduled task runs cleanmgr.exe to perform disk cleanup, which may trigger the rule due to the presence of the executable.
  Filter/Exclusion: process.name != "cleanmgr.exe" or process.parent.name != "schtasks.exe"

• Scenario: Admin using msiexec.exe to install a legitimate software update
  Description: An administrator uses msiexec.exe to deploy a software update, which may be flagged due to its association with malicious payloads.
  Filter/Exclusion: process.name != "msiexec.exe" or process.parent.name != "explorer.exe"

• Scenario: System restore or backup process using rstrui.exe
  Description: A system restore operation initiated via rstrui.exe may trigger the rule due to its execution context and file system activity.
  Filter/Exclusion: process.name != "rstrui.exe" or process.parent.name != "explorer.exe"

• Scenario: PowerShell script running a legitimate administrative task
  Description: A PowerShell script is used to perform routine administrative tasks such as user management or configuration changes, which may resemble malicious behavior.
  Filter/Exclusion: process.name != "powershell.exe" or process.parent.name != "explorer.exe" and script.name != "legitimate_script.ps1"

• Scenario: Antivirus or endpoint protection tool performing a scan
  Description: A security tool like Malwarebytes or Kaspersky performs a full system scan, which may trigger the rule due to high file activity and process spawning.
  Filter/Exclusion: process.name != "mbam.exe" or process.name != "kavservice.exe" or `