UnnamedScrambler12C12Dp0ke

Hunt Hypothesis

This rule detects the execution of a YARA signature associated with a known obfuscation or packing technique, indicating that an adversary may be using a scrambled or modified binary to evade static analysis. SOC teams should proactively hunt for this pattern to identify potentially hidden or low-fidelity malware implants that standard signature-based detections might miss due to their obfuscated nature.

YARA Rule

rule UnnamedScrambler12C12Dp0ke
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC B9 05 00 00 00 6A 00 6A 00 49 75 F9 51 53 56 57 B8 ?? 3A [2] E8 ?? EC FF FF 33 C0 55 68 [4] 64 FF 30 64 89 20 E8 ?? D7 FF FF E8 [2] FF FF B8 20 [3] 33 C9 BA 04 01 00 00 E8 ?? DB FF FF 68 04 01 00 00 68 20 [3] 6A 00 FF 15 10 [3] BA [4] B8 14 [3] E8 [2] FF FF 85 C0 0F 84 ?? 04 00 00 BA 18 [3] 8B 0D 14 [3] E8 [2] FF FF 8B 05 88 [3] 8B D0 B8 54 [3] E8 ?? E3 FF FF B8 54 [3] E8 ?? E2 FF FF 8B D0 B8 18 [3] 8B 0D 88 [3] E8 ?? D6 FF FF FF 35 34 [3] FF 35 30 [3] FF 35 3C [3] FF 35 38 [3] 8D 55 E8 A1 88 [3] E8 ?? F0 FF FF 8B 55 E8 B9 54 }

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

• Scenario: A developer or DevOps engineer uses a custom Python or Node.js script to perform data obfuscation or encoding (e.g., Base64, XOR, or custom cipher) on configuration files or logs before archiving them. The script may use in-memory string manipulation that matches the “scrambler” pattern, especially if the script is executed via python.exe or node.exe with specific arguments.

  • Filter/Exclusion: Exclude processes where the parent process is a known development tool (e.g., code.exe, idea64.exe, vscode.exe) or where the command line contains keywords like encode, obfuscate, or cipher and the working directory is within a standard development path (e.g., C:\dev\, C:\projects\).

• Scenario: An automated backup or archival job (e.g., using robocopy, 7z, or a custom PowerShell script) compresses or encrypts data using a tool that performs byte-level transformation. If the YARA rule targets specific byte patterns or string scrambles, legitimate compression algorithms (like LZMA or AES) might trigger a match if the rule is overly broad on memory or file content.

  • Filter/Exclusion: Exclude processes running from standard backup utility paths (e.g., C:\Program Files\BackupExec\, C:\Program Files\Acronis\) or where the parent process is a scheduled task service (svchost.exe with Schedule service) and the command line includes backup, archive, or compress.

• Scenario: A security scanner or antivirus tool (e.g., CrowdStrike Falcon, Carbon Black, or a custom EDR agent) performs in-memory scanning or heuristic analysis, which may involve temporarily scrambling or hashing data in memory. If the YARA rule scans process memory,