Unidentified Implant by APT29

Hunt Hypothesis

The hypothesis is that the detection identifies potential APT29 implant activity, characterized by unusual process behavior and network communication patterns indicative of a sophisticated adversary establishing a foothold. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate advanced persistent threats before they escalate to data exfiltration or system compromise.

YARA Rule

rule Unidentified_Malware_Two {
   meta:
      description = "Unidentified Implant by APT29"
      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:
      $my_string_one = "/zapoy/gate.php"
      $my_string_two = { E3 40 FE 45 FD 0F B6 45 FD 0F B6 14 38 88 55 FF 00 55
         FC 0F B6 45 FC 8A 14 38 88 55 FE 0F B6 45 FD 88 14 38 0F B6 45 FC 8A
         55 FF 88 14 38 8A 55 FF 02 55 FE 8A 14 3A 8B 45 F8 30 14 30 }
      $my_string_three = "S:\\Lidstone\\renewing\\HA\\disable\\In.pdb"
      $my_string_four = { 8B CF 0F AF CE 8B C6 99 2B C2 8B 55 08 D1 F8 03 C8
         8B 45 FC 03 C2 89 45 10 8A 00 2B CB 32 C1 85 DB 74 07 }
      $my_string_five = "fuckyou1"
      $my_string_six = "xtool.exe"
   condition:
      ($my_string_one and $my_string_two)
      or ($my_string_three or $my_string_four)
      or ($my_string_five and $my_string_six)
}

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 6 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: A system administrator is using PowerShell to run a legitimate scheduled job that performs system maintenance, such as disk cleanup or log rotation.
  Filter/Exclusion: process.parent_process_name == "schtasks.exe" or process.command_line contains "schtasks"

• Scenario: A security analyst is using PowerShell to run a script that automates the deployment of a software update, which includes the use of Invoke-Command or Start-Process.
  Filter/Exclusion: process.user == "domain\security_team" or process.command_line contains "update" or "patch"

• Scenario: A database administrator is executing a SQL Server Agent Job that uses PowerShell to back up databases, which may include the use of Invoke-Command or Start-Process.
  Filter/Exclusion: process.parent_process_name == "sqlagent.exe" or process.command_line contains "backup" or "sqlbackup"

• Scenario: A developer is using PowerShell to run a CI/CD pipeline task that includes executing scripts or binaries as part of a build process.
  Filter/Exclusion: process.user == "domain\devops_team" or process.command_line contains "build" or "ci" or "cd"

• Scenario: A system administrator is using PowerShell to run a Windows Update task that includes the use of Invoke-Command or Start-Process to apply patches.
  Filter/Exclusion: process.parent_process_name == "wuauclt.exe" or process.command_line contains "update" or "patch"