Ciphator v46 Hint DOS EP

Hunt Hypothesis

This rule identifies potential Ciphator v46 malware variants by detecting specific DOS executable entry point characteristics, indicating the presence of a legacy or obfuscated threat often used for initial access or persistence. Proactively hunting for this signature in Azure Sentinel allows the SOC to uncover dormant or overlooked executables on endpoints, reducing the risk of undetected lateral movement or data exfiltration associated with this known malware family.

YARA Rule

rule Ciphator_v46_Hint_DOS_EP: PEiD
{
    strings:
        $a = { 93 93 E8 ?? ?? 58 6A 00 0E 68 ?? ?? CF EB }
    condition:
        $a at pe.entry_point

}

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.

• Source Rule

False Positive Guidance

• Legacy DOS Utility Execution via Command Prompt

  • Scenario: An administrator runs a legacy text processing or disk utility (e.g., EDLIN.EXE, DEBUG.EXE, or DISKCOPY.EXE) from a mapped network share or local C:\Tools\Legacy\ directory to inspect or modify a specific configuration file. These small, static DOS executables often match the “Hint DOS EP” heuristic due to their minimal header structure and lack of modern PE features.
  • Filter/Exclusion: Exclude files located in known legacy tool directories (e.g., C:\Tools\, C:\Utils\, D:\LegacyApps\) and exclude processes where the parent is cmd.exe or powershell.exe if the file size is under 64KB and the extension is .exe or .com.

• Scheduled Job for Log Rotation or Cleanup

  • Scenario: A scheduled task (e.g., LogCleaner) executes a small DOS-based cleanup script or utility (e.g., DEL.EXE wrapper or a custom 16-bit .exe) to rotate IIS or application logs. The binary is a simple DOS stub that calls standard Windows APIs, triggering the YARA rule due to its basic DOS MZ header and lack of rich PE metadata.
  • Filter/Exclusion: Exclude executions where the process name matches known cleanup utilities (e.g., clean.exe, rotate.exe, logclean.exe) and the parent process is svchost.exe (Task Scheduler) or schtasks.exe. Additionally, exclude if the file path contains logs, temp, or backup.

• Embedded DOS Stubs in Installer Packages

  • Scenario: An enterprise software installer (e.g., for legacy CAD or accounting software) extracts a small DOS-based