Sednit / EVILTOSS Implant by APT28

Hunt Hypothesis

The detection identifies potential Sednit / EVILTOSS Implant activity by APT28, characterized by suspicious network communications and command-and-control behavior indicative of a persistent, stealthy adversary. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced persistent threats before they exfiltrate data or escalate within the network.

YARA Rule

rule IMPLANT_6_v6 {
   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:
      $Init1_fun = {68 10 27 00 00 FF 15 ?? ?? ?? ?? A1 ?? ?? ?? ?? 6A FF 50
         FF 15 ?? ?? ?? ?? 33 C0 C3}
   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 1 string patterns in its detection logic.

References

False Positive Guidance

Scenario: Legitimate System Update via Windows Update
Description: A Windows update process may include binaries with similar hashes to the malicious implant due to false positives in signature databases.
Filter/Exclusion: Check the process name and command line for wuauclt.exe or Windows Update related strings. Exclude events where the process is initiated by svchost.exe or wuauserv.
Scenario: Scheduled Job for Log Collection
Description: A legitimate scheduled task may use a tool like LogParser or PowerShell to collect logs, which could trigger the rule due to similar behavior.
Filter/Exclusion: Filter by process name LogParser.exe or powershell.exe with command lines containing log or Collect-EventLog. Exclude tasks with known log collection tools.
Scenario: Admin Task Using PsExec for Remote Execution
Description: System administrators may use PsExec to remotely execute commands, which can mimic the behavior of the implant.
Filter/Exclusion: Filter by process name psexec.exe and check for admin privileges. Exclude events where the command line includes –s or –i flags used for remote execution.
Scenario: Malware Analysis Environment
Description: In a sandbox or malware analysis environment, benign tools like Process Hacker or Wireshark may be used, which could trigger the rule due to similar process behaviors.
Filter/Exclusion: Check for presence of sandbox detection tools or environment markers like sandboxed or vmware. Exclude processes running in a known analysis environment.
Scenario: Antivirus or EDR Tool Behavior
Description: Antivirus or EDR tools may perform deep scans or memory analysis, which can resemble the implant’s behavior.
**Filter/