HAMMERTOSS / HammerDuke Implant by APT29

Hunt Hypothesis

The detection identifies potential APT29 activity involving the HAMMERTOSS / HammerDuke implant, which is associated with advanced persistent threats and covert command and control operations. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate early-stage compromise by a sophisticated adversary.

YARA Rule

rule IMPLANT_8_v2 {
   meta:
      description = "HAMMERTOSS / HammerDuke 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:
      $DOTNET= "mscorlib" ascii
      $XOR = {61 20 AA 00 00 00 61}
   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

• 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 scheduled task runs a script that includes the string “HammerDuke” due to a naming convention or documentation.
  Filter/Exclusion: Exclude processes initiated by the Task Scheduler with CommandLine containing /s or --scheduled.

• Scenario: Admin PowerShell Script for Patch Management
  Description: An admin uses a PowerShell script named “HammerDuke.ps1” to automate patching, which includes the string “HammerDuke” in the script name.
  Filter/Exclusion: Exclude processes with ProcessName equal to powershell.exe and CommandLine containing -File or -Command with a known admin script path.

• Scenario: Legitimate Tool Named “HammerDuke” Used for DevOps
  Description: A DevOps tool or CI/CD pipeline is named “HammerDuke” and is used for deployment automation.
  Filter/Exclusion: Exclude processes with ProcessName matching a known DevOps tool (e.g., jenkins.exe, git.exe) or with CommandLine containing a known CI/CD command.

• Scenario: Log File Parsing or Monitoring Tool
  Description: A log analysis tool or SIEM system includes the term “HammerDuke” in its configuration or log output for internal reference.
  Filter/Exclusion: Exclude processes with ProcessName matching known log analysis tools (e.g., splunkd.exe, logstash.exe) or with CommandLine containing --config or --log.

• Scenario: False Positive from a Security Tool’s Own Logs
  Description: A security tool (e.g., EDR, SIEM) generates logs that include the term “HammerDuke” in its internal diagnostics or alerts.