UPXFreakV01HMX0101

Hunt Hypothesis

This YARA rule targets specific file patterns associated with the UPXFreakV01HMX0101 signature, potentially indicating the presence of a low-severity malware variant or suspicious executable artifact within the environment. Proactively hunting for this indicator allows the SOC team to identify dormant or stealthy threats that may have evaded standard behavioral detections, ensuring early containment in the Azure Sentinel environment.

YARA Rule

rule UPXFreakV01HMX0101
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE [4] 83 C6 01 FF E6 00 00 }

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 DevOps engineer uses a YARA scanner (e.g., yara CLI or yara-python) to audit application binaries or configuration files in a staging environment. The scanner process itself loads the rule file into memory, and if the rule contains specific string literals or metadata that match the detection logic, the scanner process may be flagged.
  • Filter/Exclusion: Exclude processes where the parent process is yara.exe, yara64.exe, or python.exe (if running yara-python) and the command line contains arguments like -r, --rules, or paths ending in .yar/.yara.
• Scenario: An IT administrator performs a manual integrity check on a critical application binary using a tool like PEiD, ExifTool, or a custom PowerShell script that reads file headers. If the detection logic triggers on specific byte patterns or string constants found in the file header or metadata, the reading process (e.g., powershell.exe or peid.exe) might be caught if the rule inspects process memory or loaded modules.
  • Filter/Exclusion: Exclude processes named powershell.exe, pwsh.exe, peid.exe, or exiftool.exe when the command line includes flags like -h, -info, or paths to specific binary files, and the user account belongs to the IT_Admins or DevOps group.
• Scenario: A scheduled backup or snapshot job (e.g., Veeam, Commvault, or Windows Server Backup) creates a temporary copy of a large application binary or database file in a temp directory (%TEMP% or C:\Windows\Temp). If the detection logic is sensitive to file location or specific string patterns in the file content, the backup agent process (e.g., `vss