Sednit / EVILTOSS Implant by APT28

Hunt Hypothesis

The detection identifies potential deployment of the Sednit / EVILTOSS implant by APT28, indicating adversary presence within the network. SOC teams should proactively hunt for this behavior to detect and mitigate advanced persistent threats leveraging this sophisticated malware in their Azure Sentinel environment.

YARA Rule

rule IMPLANT_6_v1
{
   meta:
      description = "Sednit / EVILTOSS 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 = "dll.dll" wide ascii
      $STR2 = "Init1" wide ascii
      $STR3 = "netui.dll" wide ascii
   condition:
      (uint16(0) == 0x5A4D or uint16(0) == 0xCFD0 or uint16(0) == 0xC3D4 or
      uint32(0) == 0x46445025 or uint32(1) == 0x6674725C) 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 3 string patterns in its detection logic.

References

False Positive Guidance

Scenario: Scheduled System Maintenance Task
Description: A legitimate scheduled task using schtasks.exe to perform system maintenance (e.g., disk cleanup, log rotation) may trigger the rule due to similar command-line patterns.
Filter/Exclusion: Check for schtasks.exe with known maintenance task names (e.g., DiskCleanup, LogClear) and exclude based on command-line arguments or scheduled task names.
Scenario: PowerShell Script for Admin Task
Description: A PowerShell script used by administrators to configure system settings (e.g., Set-ItemProperty, Get-Service) may trigger the rule due to similar string patterns.
Filter/Exclusion: Filter based on the presence of powershell.exe with known admin scripts or use a regex to exclude common admin commands like Set-ItemProperty or Get-Service.
Scenario: Antivirus or Endpoint Protection Scan
Description: A legitimate antivirus or endpoint protection tool (e.g., Bitdefender, Kaspersky) may trigger the rule when scanning for malware signatures or performing integrity checks.
Filter/Exclusion: Exclude processes associated with known security tools (e.g., bdagent.exe, kavsvc.exe) or filter based on process names and parent processes.
Scenario: Software Update or Patch Deployment
Description: A legitimate software update or patch deployment (e.g., using msiexec.exe, setup.exe) may trigger the rule due to similar command-line execution patterns.
Filter/Exclusion: Exclude processes related to known update mechanisms (e.g., msiexec.exe, setup.exe) or filter based on file paths associated with enterprise patching tools.
Scenario: Database Backup or Restore Job
Description: A database backup or restore job (e.g., using `sqlcmd.exe