IMPPacker10MahdiHezavehiIMPOSTER

Hunt Hypothesis

This detection identifies potential adversary activity involving the use of a specific malicious packer signature (IMPPacker10MahdiHezavehi) that may indicate the execution of obfuscated malware designed to evade standard static analysis. The SOC team should proactively hunt for this behavior in Azure Sentinel to uncover stealthy threats that leverage custom packing techniques, ensuring early identification before these low-severity indicators escalate into significant compromises.

YARA Rule

rule IMPPacker10MahdiHezavehiIMPOSTER
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 28 [3] 00 00 00 00 00 00 00 00 40 [3] 34 [3] 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4C [3] 5C [3] 00 00 00 00 [8] 00 00 00 00 4B 45 52 4E 45 4C 33 32 2E 64 6C 6C 00 00 47 65 74 50 72 6F 63 }

condition:
		$a0
}

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

Here are 5 specific false positive scenarios for the IMPPacker10MahdiHezavehiIMPOSTER detection rule, along with recommended filters or exclusions:

• Scenario: Legitimate Software Deployment via SCCM/Intune

  • Context: When System Center Configuration Manager (SCCM) or Microsoft Intune deploys a new application package to endpoints, the deployment engine often utilizes a custom packer to compress and sign the installer payload. This process mimics the “IMPOSTER” behavior by creating temporary packed executables that match the YARA signature before extraction.
  • Filter/Exclusion: Exclude processes where ImageName matches ccmsetup.exe, Microsoft.Workplace.JoinedService.exe, or IntuneManagementExtension.exe. Additionally, filter out events where the parent process is a known deployment service (e.g., wuauserv.exe) and the file hash matches a trusted baseline in your asset inventory.

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Major security vendors like CrowdStrike Falcon or Symantec Endpoint Protection frequently use proprietary packers to bundle daily definition updates. When these agents download and unpack new signatures, they generate temporary executables that trigger the IMPOSTER rule due to their compressed structure and specific header patterns.
  • Filter/Exclusion: Create an exclusion for file paths containing \Program Files\ or \ProgramData\ directories belonging to known security vendors (e.g., C:\Program Files\CrowdStrike\, C:\ProgramData\Symantec). Filter events where the process name matches csfalcon.exe, Symantec Antivirus Client, or rtvscan64.exe.

• Scenario: CI/CD Pipeline Artifact Generation

  • Context: In DevOps environments, tools like Jenkins, GitLab Run