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_v7 {
   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 = "Init1"
      $OPT1 = "ServiceMain"
      $OPT2 = "netids" nocase wide ascii
      $OPT3 = "netui" nocase wide ascii
      $OPT4 = "svchost.exe" wide ascii
      $OPT5 = "network" nocase wide ascii
   condition:
      (uint16(0) == 0x5A4D or uint16(0) == 0xCFD0 or uint16(0) == 0xC3D4 or
      uint32(0) == 0x46445025 or uint32(1) == 0x6674725C) and $STR1 and 2 of ($OPT*)
}

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 6 string patterns in its detection logic.

References

False Positive Guidance

Scenario: Scheduled System Maintenance Task
Description: A legitimate scheduled task running a script that includes the string “eviltoSS” due to a naming convention or a misconfigured script.
Filter/Exclusion: Check for process.name containing “schtasks.exe” or “Task Scheduler” and filter out processes with process.parent.name equal to “schtasks.exe”.
Scenario: Admin Performing PowerShell Script for Patching
Description: An administrator runs a PowerShell script that includes the term “eviltoSS” in a comment or variable name as part of a patching routine.
Filter/Exclusion: Filter processes where process.name is “powershell.exe” and process.parent.name is “cmd.exe” or “explorer.exe”, and check for script.name or script.content indicating patching activity.
Scenario: Log Management Tool Processing Logs
Description: A log management tool (e.g., Splunk, ELK Stack) processes logs and includes the term “eviltoSS” in its log parsing configuration.
Filter/Exclusion: Filter events where source is a known log management tool or process.name is “splunkd.exe”, “logstash.exe”, or “kibana.exe”.
Scenario: Internal Security Tool for Threat Hunting
Description: A threat hunting tool (e.g., CrowdStrike Falcon, Microsoft Defender ATP) uses the term “eviltoSS” in its query or rule set for testing.
Filter/Exclusion: Filter events where process.name is a known security tool (e.g., “falcon.exe”, “microsoftdefender.exe”) or check for rule.name containing “test” or “hunting”.
Scenario: User-Initiated File Upload with Malformed Name
Description: A user