Downrage Implant by APT28

Hunt Hypothesis

The Downrage Implant by APT28 is associated with advanced persistent threat actors who use it for long-term system control and data exfiltration. SOC teams should proactively hunt for this implant in Azure Sentinel to detect and mitigate early-stage APT28 campaigns before significant data loss or network compromise occurs.

YARA Rule

rule IMPLANT_1_v1 {
   meta:
      description = "Downrage 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:
      $STR1 = {6A ?? E8 ?? ?? FF FF 59 85 C0 74 0B 8B C8 E8 ?? ?? FF FF 8B F0
         EB 02 33 F6 8B CE E8 ?? ?? FF FF 85 F6 74 0E 8B CE E8 ?? ?? FF FF 56
         E8 ?? ?? FF FF 59}
   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 1 string patterns in its detection logic.

References

• https://www.us-cert.gov/ncas/current-activity/2017/02/10/Enhanced-Analysis-GRIZZLY-STEPPE
• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate system maintenance task, such as Windows Task Scheduler running a script for disk cleanup or log rotation, may trigger the rule due to similar process or file behavior.
  Filter/Exclusion: Exclude processes associated with Task Scheduler or files located in system directories like C:\Windows\Tasks or C:\Windows\System32.

• Scenario: Admin Performing PowerShell Script for Patch Management
  Description: An administrator may run a PowerShell script to apply patches or update software, which could resemble the behavior of the Downrage Implant.
  Filter/Exclusion: Exclude processes initiated by PowerShell.exe with command-line arguments related to patching or updates, or filter by user accounts with administrative privileges.

• Scenario: Legitimate Use of Cobalt Strike Beacon
  Description: Security teams may use Cobalt Strike Beacon for red teaming or penetration testing, which could trigger the rule due to similar network or process behavior.
  Filter/Exclusion: Exclude processes with known Cobalt Strike signatures, or filter by user accounts associated with security testing teams.

• Scenario: Automated Backup Job Using Veeam or Acronis
  Description: Automated backup jobs using tools like Veeam or Acronis may involve file system access and network communication that could be mistaken for malicious activity.
  Filter/Exclusion: Exclude processes related to backup tools, such as Veeam.Backup.Runner.exe or AcronisBackupService.exe, or filter by directories used for backups.

• Scenario: User Running Malware Analysis Tools
  Description: A security analyst may run malware analysis tools like Cuckoo Sandbox or Joe Sandbox, which can exhibit behaviors similar to the Downrage Implant.
  Filter/Exclusion: Exclude processes associated with sandboxing tools or filter by user accounts