TPACKv05cm1

Hunt Hypothesis

This detection identifies specific file artifacts matching the TPACKv05cm1 signature to uncover potential early-stage adversary activity involving custom or obfuscated payloads within the Azure environment. Proactive hunting for this rule is essential to validate false positives and establish a baseline of legitimate traffic, ensuring that low-severity indicators do not mask more sophisticated threats in the broader security posture.

YARA Rule

rule TPACKv05cm1
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 68 [2] FD 60 BE [2] BF [2] B9 [2] F3 A4 8B F7 BF [2] FC 46 E9 8E FE }

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

Here are 4 specific false positive scenarios for the TPACKv05cm1 detection rule, tailored to a legitimate enterprise environment:

• Scenario: Scheduled Microsoft Office Click-to-Run Updates

  • Context: The OfficeC2RClient.exe process frequently executes in the background during business hours or overnight maintenance windows to apply cumulative updates. This activity often involves unpacking compressed update payloads that match the TPACK signature logic, triggering an alert even though it is a standard vendor operation.
  • Suggested Filter: Exclude processes where ProcessName equals OfficeC2RClient.exe AND ParentProcessName equals svchost.exe (or msiexec.exe) running under the SYSTEM or specific service account context within the Program Files\Microsoft Office directory.

• Scenario: Antivirus Real-Time Scanning of Archive Extraction

  • Context: Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon or Symantec Endpoint Protection often spawn temporary worker threads to extract .zip, .cab, or .7z files for scanning. When these tools unpack large archives containing executable binaries, the extraction logic mimics the behavior of a malicious package unpacker, causing the YARA rule to fire.
  • Suggested Filter: Create an exclusion for processes with ImageHash matching known good hashes for FalconSensor.exe, Symantec Antivirus Console.exe, or Sophos Anti-Virus.exe, specifically when the parent process is the antivirus engine itself and the file path contains \Temp\ or \Quarantine\.

• Scenario: Deployment of Software via SCCM/Intune

  • Context: During scheduled deployment windows, Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune pushes application packages to endpoints. The