EXEPACKLINKv360v364v365or50121

Hunt Hypothesis

This rule identifies executable files packed with specific Linker versions (v360, v364, v365, or 50121), a technique often employed by adversaries to obfuscate malware binaries and evade static signature-based detection. Proactively hunting for these specific packing characteristics allows the SOC to uncover stealthy payloads that may be executing in the environment before they trigger more complex behavioral alerts.

YARA Rule

rule EXEPACKLINKv360v364v365or50121
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 8C C0 05 [2] 0E 1F A3 [2] 03 [3] 8E C0 8B [3] 8B ?? 4F 8B F7 FD F3 A4 50 B8 [2] 50 CB }

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: Legitimate software installation or update via Microsoft System Center Configuration Manager (SCCM) or Intune, where the installer executable (e.g., setup.exe or msiexec.exe) is packed with a commercial packer like UPX or Aspack to reduce size and protect IP.
  • Filter/Exclusion: Exclude processes where the parent process is ccmsetup.exe, ccmexec.exe, or msiexec.exe, and the file path contains \Windows\CCM\ or \Program Files\Microsoft Configuration Manager\.
• Scenario: Execution of a signed, known-good vendor application (e.g., Adobe Creative Cloud, Oracle Java, or Symantec Endpoint Protection) that uses a commercial packer (such as Aspack, FSG, or PECompact) for its main executable or update agent.
  • Filter/Exclusion: Exclude files with a valid digital signature from a trusted vendor (e.g., Adobe Inc., Oracle Corporation, Symantec) and where the file path resides in standard installation directories like \Program Files\ or \Program Files (x86)\.
• Scenario: A scheduled task or service running a utility tool (e.g., 7zG.exe for 7-Zip, WinRAR.exe, or Ninite.exe) that is packed to optimize startup time or protect the binary, often triggered by user login or system boot.
  • Filter/Exclusion: Exclude processes where the command line contains arguments typical of archive managers or installers (e.g., a, x, t, i) and the file name matches known utility binaries (7z*.exe, WinRAR.exe, Ninite.exe).
• Scenario: Execution of a .NET application or C++ binary compiled with a specific linker or packer (