EPExEPackV10EliteCodingGroup

Hunt Hypothesis

This hypothesis targets the presence of executable files packed with the EPExEPack V10 Elite variant, a technique often employed by adversaries to obfuscate malware payloads and evade static analysis. Proactively hunting for this specific packing signature in Azure Sentinel allows the SOC team to identify potentially compromised assets or staged payloads before they execute, reducing the risk of undetected lateral movement or persistence.

YARA Rule

rule EPExEPackV10EliteCodingGroup
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 68 [4] B8 [4] FF 10 }

condition:
		$a0 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

• Scenario: A developer or IT administrator manually packs a custom C/C++ utility using the UPX (Ultimate Packer for eXecutables) tool with the --elite or specific compression options to reduce binary size for deployment. The resulting executable contains the characteristic byte sequences or structural markers that the EPExEPackV10EliteCodingGroup YARA rule is designed to detect.

  • Filter/Exclusion: Exclude files located in known development directories (e.g., C:\Dev\, C:\Projects\) or exclude executables with a specific hash allowlist if the packed binary is a known, signed internal tool. Alternatively, exclude processes where the parent process is a compiler or build tool (e.g., msbuild.exe, cmake.exe).

• Scenario: A legacy line-of-business (LOB) application or a specific vendor-provided agent (e.g., a monitoring agent or a custom backup utility) is distributed as a packed executable to protect intellectual property or reduce installation size. The vendor does not re-sign the packed binary, causing it to match the YARA signature during routine file scans.

  • Filter/Exclusion: Create a specific exclusion for the known vendor’s installation directory (e.g., C:\Program Files\VendorApp\bin\) or exclude the specific file name if it is unique to that vendor. Ensure the exclusion is scoped to the specific directory to avoid broadening the attack surface.

• Scenario: An automated software deployment pipeline (e.g., using SCCM, Intune, or Chocolatey) installs a third-party application that uses UPX packing for its installer or main executable. The installation process drops the packed binary into the system drive, triggering the detection rule before the file is potentially unpacked or executed in a controlled context.

  • Filter/Exclusion: Exclude files created by known deployment