LockProg v05a Hint DOS EP

Hunt Hypothesis

This hypothesis targets the presence of the LockProg v05a malware variant, a known ransomware strain that utilizes a DOS executable entry point to establish initial foothold or execute payload delivery. Proactively hunting for this specific signature in Azure Sentinel allows the SOC to identify compromised endpoints early, potentially preventing the encryption of critical data before the ransomware completes its execution cycle.

YARA Rule

rule LockProg_v05a_Hint_DOS_EP: PEiD
{
    strings:
        $a = { E8 ?? ?? E8 ?? ?? E8 ?? ?? BF ?? ?? 8B EC 8B ?? ?? 2E ?? ?? ?? 03 F9 89 0D B4 30 CD 21 3C 02 73 ?? B4 4C CD 21 }
    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-Based Utility Execution: Administrators frequently use legacy DOS executables (e.g., DISKCOPY.EXE, FORMAT.COM, or custom internal maintenance scripts) to perform low-level disk operations or firmware updates on edge devices or legacy servers. These binaries often reside in C:\Windows\System32 or specific maintenance directories and may match the “DOS EP” (Entry Point) heuristic due to their 16-bit or MZ header structure.

  • Filter/Exclusion: Exclude files located in C:\Windows\System32\ or C:\Program Files\LegacyTools\ where the parent process is a known administrative tool (e.g., cmd.exe, powershell.exe, or taskmgr.exe) and the file size is less than 50KB.

• Scheduled Maintenance Job for Firmware/BIOS Updates: Enterprise environments often schedule automated jobs using Task Scheduler to run vendor-specific DOS-based update utilities (e.g., AMI_APT.EXE for American Megatrends, or Insyde update tools) during maintenance windows. These executables are typically small, DOS-based, and executed from network shares or local admin shares.

  • Filter/Exclusion: Exclude execution if the parent process is svchost.exe (specifically the Task Scheduler service) or schtasks.exe, and the file path contains keywords like firmware, bios, update, or vendor (e.g., C:\Admin\BIOS_Update\).

• Antivirus/EDR Quarantine or Scanning Artifacts: Some AV/EDR solutions (e.g., CrowdStrike, SentinelOne, or legacy McAfee) may create temporary DOS-based stubs or quarantine containers that are briefly executed or scanned. These artifacts might be placed in temp directories (%TEMP%, `C:\Windows