UnnamedScrambler11Cp0ke

Hunt Hypothesis

This detection identifies potential file obfuscation or packing activities where a process utilizes an unnamed scrambler to modify executable structures, often indicative of malware attempting to evade static analysis. SOC teams should proactively hunt for this behavior in Azure Sentinel to uncover stealthy threats that may bypass traditional signature-based defenses by analyzing the specific YARA matches across endpoint logs and correlating them with subsequent network or process anomalies.

YARA Rule

rule UnnamedScrambler11Cp0ke
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 E4 53 56 33 C0 89 45 E4 89 45 E8 89 45 EC B8 C0 47 00 10 E8 4F F3 FF FF BE 5C 67 00 10 33 C0 55 68 D2 4A 00 10 64 FF 30 64 89 20 E8 EB DE FF FF E8 C6 F8 FF FF BA E0 4A 00 10 B8 CC 67 00 10 E8 5F F8 FF FF 8B D8 8B D6 8B C3 8B 0D CC 67 00 10 E8 3A DD FF FF 8B 46 50 8B D0 B8 D4 67 00 10 E8 5B EF FF FF B8 D4 67 00 10 E8 09 EF FF FF 8B D0 8D 46 14 8B 4E 50 E8 14 DD FF FF 8B 46 48 8B D0 B8 D8 67 00 [5] FF B8 D8 67 00 10 E8 E3 EE FF FF 8B D0 8B C6 8B 4E 48 E8 EF DC FF FF FF 76 5C FF 76 58 FF 76 64 FF 76 60 B9 D4 67 00 10 8B 15 D8 67 00 10 A1 D4 67 00 10 E8 76 F6 FF FF A1 D4 67 00 10 E8 5C EE FF FF 8B D0 B8 CC 67 00 10 E8 CC F7 FF FF 8B D8 B8 DC 67 00 10 }

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 UnnamedScrambler11Cp0ke YARA detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Endpoint Protection Scanning

  • Context: The rule triggers when the primary endpoint protection agent (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or Carbon Black) performs its scheduled signature update scan. These agents often inject obfuscated scanning modules that match the Scrambler pattern in memory or on disk.
  • Filter/Exclusion: Exclude processes where the parent process is the specific AV service (e.g., C:\Program Files\CrowdStrike\fs_qc.exe) and the file path resides within the vendor’s installation directory (C:\Program Files\CrowdStrike\ or C:\ProgramData\Microsoft\Windows Defender).

• Scenario: Scheduled Group Policy Script Execution

  • Context: During business hours, a scheduled Group Policy Object (GPO) triggers a PowerShell script that downloads and executes a configuration utility. If this utility uses a packed installer or an obfuscated script engine (common in tools like PDQ Deploy or Ansible), it may trigger the Scrambler signature due to its compressed payload structure.
  • Filter/Exclusion: Create a rule exclusion for files executed by powershell.exe where the command line contains specific GPO identifiers (e.g., /s /v "GPO_ID_12345") and the file hash matches known good hashes of the enterprise configuration utility.

• Scenario: Enterprise Backup Agent Activity

  • Context: The detection fires when backup agents like Veeam Backup & Replication or Rubrik perform incremental scans. These tools often utilize obfuscation techniques to compress and