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 data exfiltration. 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_v1
{
   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
      $REF_URL = "https://www.google.com/url?sa=" wide
      $REF_var_1 = "&rct=" wide
      $REF_var_2 = "&q=&esrc=" wide
      $REF_var_3 = "&source=" wide
      $REF_var_4 = "&cd=" wide
      $REF_var_5 = "&ved=" wide
      $REF_var_6 = "&url=" wide
      $REF_var_7 = "&ei=" wide
      $REF_var_8 = "&usg=" wide
      $REF_var_9 = "&bvm=" wide
      $REF_value_1 = "QFj" wide
      $REF_value_2 = "bv.81" wide
   condition:
      (uint16(0) == 0x5A4D) and ($DOTNET) and ($REF_URL) and
      (3 of ($REF_var*)) and (1 of ($REF_value*))
}

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 13 string patterns in its detection logic.

References

False Positive Guidance

Scenario: Legitimate Windows Task Scheduler Job
Description: A scheduled task is configured to run a script that includes the string “HammerDuke” as part of a naming convention or logging.
Filter/Exclusion: Check for CommandLine containing schtasks.exe or Task Scheduler in the process tree, and exclude entries where the command line includes --name or --description with known legitimate task names.
Scenario: PowerShell Script for System Monitoring
Description: A system admin uses a PowerShell script named “HammerDuke.ps1” to monitor system performance, which includes the string “HammerDuke” in the script name.
Filter/Exclusion: Filter by ProcessName equal to powershell.exe and check for ScriptBlockText containing “monitor” or “performance” to distinguish from malicious activity.
Scenario: Admin Tool for Network Discovery
Description: A network discovery tool like Nmap or Masscan is used by the security team, and the output includes the term “HammerDuke” in a log file due to a misconfiguration.
Filter/Exclusion: Exclude entries where the ProcessName is nmap.exe or masscan.exe, or where the file path contains logs/ or output/.
Scenario: Legitimate Software Update Process
Description: A software update process (e.g., using Chocolatey or WSUS) includes a package named “HammerDuke” as part of a naming convention for internal tools.
Filter/Exclusion: Filter by ProcessName containing choco.exe or wsusutil.exe, and exclude entries where the package name includes “internal” or “tool”.
Scenario: Log File Parsing with String Matching