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.

YARA Rule

rule IMPLANT_6_v2 {
   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:
      $obf_func = { 8B 45 F8 6A 07 03 C7 33 D2 89 45 E8 8D 47 01 5B 02 4D 0F F7 F3 6A 07 8A 04 32 33 D2 F6 E9 8A C8 8B C7 F7 F3 8A 44 3E FE 02 45 FC 02 0C 32 B2 03 F6 EA 8A D8 8D 47 FF 33 D2 5F F7 F7 02 5D 14 8B 45 E8 8B 7D F4 C0 E3 06 02 1C 32 32 CB 30 08 8B 4D 14 41 47 83 FF 09 89 4D 14 89 7D F4 72 A1 }
   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: Scheduled System Maintenance Task
Description: A legitimate system maintenance task, such as schtasks.exe running a cleanup job, may trigger the rule due to similar process behavior.
Filter/Exclusion: Check for ProcessName containing schtasks.exe and CommandLine containing /create or /run with known maintenance job names.
Scenario: Admin Performing PowerShell Script for Patching
Description: An administrator using PowerShell to deploy patches or updates may trigger the rule due to similar script execution patterns.
Filter/Exclusion: Filter by ProcessName containing powershell.exe and CommandLine containing -File or -Command with known patching scripts or paths like C:\Windows\System32\WindowsPowerShell\v1.0\.
Scenario: Logon Script Execution
Description: A logon script executed via Group Policy or local policy may trigger the rule due to similar process creation and execution patterns.
Filter/Exclusion: Filter by ProcessName containing cmd.exe or powershell.exe and CommandLine containing logonscript or gpresult.
Scenario: Antivirus or EDR Tool Scanning
Description: A legitimate antivirus or EDR tool, such as Microsoft Defender or CrowdStrike, may trigger the rule during a scan or threat hunting activity.
Filter/Exclusion: Filter by ProcessName containing MsMpEng.exe, Csrss.exe, or frsupdsvc.exe and check for known EDR tool paths.
Scenario: Database Backup Job Execution
Description: A scheduled database backup job using tools like sqlbackup.exe or mysqldump may trigger the rule due to similar process creation and command-line arguments.
Filter/Exclusion: