pscrambler12byp0ke

Hunt Hypothesis

This hunt hypothesis targets adversaries utilizing the PSCRAMBLER obfuscation technique to conceal malicious PowerShell scripts from static analysis and signature-based detection. Proactively hunting for this behavior in Azure Sentinel is critical because obfuscated scripts often bypass initial security controls, requiring dynamic behavioral analysis to uncover hidden command execution patterns that standard rules might miss.

YARA Rule

rule pscrambler12byp0ke
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC B9 04 00 00 00 6A 00 6A 00 49 75 F9 51 53 [4] 10 E8 2D F3 FF FF 33 C0 55 68 E8 31 00 10 64 FF 30 64 89 20 8D 45 E0 E8 53 F5 FF FF 8B 45 E0 8D 55 E4 E8 30 F6 FF FF 8B 45 E4 8D 55 E8 E8 A9 F4 FF FF 8B 45 E8 8D 55 EC E8 EE F7 FF FF 8B 55 EC B8 C4 54 00 10 E8 D9 EC FF FF 83 3D C4 54 00 10 00 0F 84 05 01 00 00 80 3D A0 40 00 10 00 74 41 A1 C4 54 00 10 E8 D9 ED FF FF E8 48 E0 FF FF 8B D8 A1 C4 54 00 10 E8 C8 ED FF FF 50 B8 C4 54 00 10 E8 65 EF FF FF 8B D3 59 E8 69 E1 FF FF 8B C3 E8 12 FA FF FF 8B C3 E8 33 E0 FF FF E9 AD 00 00 00 B8 05 01 00 00 E8 0C E0 FF FF 8B D8 53 68 05 01 00 00 E8 57 F3 FF FF 8D 45 DC 8B D3 E8 39 ED FF FF 8B 55 DC B8 14 56 00 10 B9 00 32 00 10 E8 BB ED FF FF 8B 15 14 56 00 10 B8 C8 54 00 10 E8 53 E5 FF FF BA 01 00 00 00 B8 C8 54 00 10 E8 8C E8 FF FF E8 DF E0 FF FF 85 C0 75 52 6A 00 A1 C4 54 00 10 E8 3B ED FF FF 50 B8 C4 54 00 10 E8 D8 EE FF FF 8B D0 B8 C8 54 00 10 59 E8 3B E6 FF FF E8 76 E0 FF FF B8 C8 54 00 10 E8 4C E6 FF FF E8 67 E0 FF FF 6A 00 6A 00 6A 00 A1 14 56 00 10 E8 53 EE FF FF 50 6A 00 6A 00 E8 41 F3 FF FF 80 3D 9C 40 00 10 00 74 05 E8 EF FB FF FF 33 C0 5A 59 59 64 89 10 68 EF 31 00 10 8D 45 DC BA 05 00 00 00 E8 7D EB FF FF C3 E9 23 E9 FF FF EB EB 5B E8 63 EA FF FF 00 00 00 FF FF FF FF 08 00 00 00 74 65 6D 70 2E 65 78 65 }

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 5 specific false positive scenarios for the pscrambler12byp0ke YARA rule, including targeted filters and exclusions:

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: During scheduled maintenance windows, Microsoft Endpoint Configuration Manager (SCCM) or Intune pushes updates to endpoints. The deployment agent (ccmsetup.exe or Microsoft.Workplace.Join) often invokes PowerShell scripts that dynamically generate obfuscated code blocks to handle complex logic, triggering the YARA signature for script scrambling patterns.
  • Filter/Exclusion: Create a whitelist exclusion based on the parent process name and path: Exclude if Parent Process Name is 'ccmsetup.exe' or 'Microsoft.Workplace.Join' AND Path starts with 'C:\Program Files (x86)\Microsoft Configuration Manager\'.

• Scenario: CI/CD Pipeline Execution by Jenkins/GitLab Runner

  • Context: In DevOps environments, build agents (e.g., java.exe running a GitLab Runner or Jenkins node) execute PowerShell scripts to compile code and run unit tests. These scripts frequently utilize inline base64-encoded commands for security context switching, which the rule interprets as potential obfuscation attempts by an attacker.
  • Filter/Exclusion: Implement a logic filter: Exclude if Parent Process Name is 'java.exe' AND Command Line contains '-agent' OR Path matches 'C:\ProgramData\GitLab\runner\'.

• Scenario: Scheduled Inventory and Compliance Scans (Qualys/Tanium)

  • Context: Enterprise asset management tools like Qualys Cloud Agent or Tanium Sensor run hourly inventory scans. These agents utilize PowerShell to query system configurations and generate reports, often employing encoded strings to ensure data integrity during transmission, which mimics the behavior of a script scrambler.
  • **Filter/