UnnamedScrambler20p0ke

Hunt Hypothesis

This rule detects the execution of the UnnamedScrambler20p0ke YARA signature, which typically identifies low-level obfuscated payloads or custom malware families that may bypass standard behavioral detections. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify stealthy, low-severity threats that could serve as initial access vectors or persistence mechanisms before they escalate to more impactful adversary actions.

YARA Rule

rule UnnamedScrambler20p0ke
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC B9 0A 00 00 00 6A 00 6A 00 49 75 F9 53 56 57 B8 1C 2F 40 00 E8 C8 F1 FF FF 33 C0 55 68 FB 33 40 00 64 FF 30 64 89 20 BA 0C 34 40 00 B8 E4 54 40 00 E8 EF FE FF FF 8B D8 85 DB 75 07 6A 00 E8 5A F2 FF FF BA E8 54 40 00 8B C3 8B 0D E4 54 40 00 E8 74 E2 FF FF C7 05 20 6B 40 00 09 00 00 00 BB 98 69 40 00 C7 45 EC E8 54 40 00 C7 45 E8 31 57 40 00 C7 45 E4 43 60 40 00 BE D3 6A 40 00 BF E0 6A 40 00 83 7B 04 00 75 0B 83 3B 00 0F 86 AA 03 00 00 EB 06 0F 8E A2 03 00 00 8B 03 8B D0 B8 0C 6B 40 00 E8 C1 EE FF FF B8 0C 6B 40 00 E8 6F EE FF FF 8B D0 8B 45 EC 8B 0B E8 0B E2 FF FF 6A 00 6A 1E 6A 00 6A 2C A1 0C 6B 40 00 E8 25 ED FF FF 8D 55 E0 E8 15 FE FF FF 8B 55 E0 B9 10 6B 40 00 A1 0C 6B 40 00 }

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: Automated Code Obfuscation in CI/CD Pipelines

  • Context: A DevOps pipeline uses a build tool (e.g., webpack, terser, or a custom Python script) that applies string scrambling or obfuscation to JavaScript/TypeScript bundles before deployment to production. The YARA rule matches the specific byte patterns of the scrambled output artifacts stored in the artifact repository or temporary build directories.
  • Filter/Exclusion: Exclude file paths matching */node_modules/*, */dist/*, */build/*, or */artifacts/* where the file extension is .js, .map, or .bundle. Additionally, exclude processes originating from node.exe, python.exe, or npm.exe if the detection is process-based.

• Scenario: Legacy Application Update with Custom Loader

  • Context: An enterprise internal application (e.g., a proprietary ERP module or legacy Java app) uses a custom loader that scrambles its configuration files or embedded resources during the update process to prevent casual reverse engineering. The update service (e.g., UpdateService.exe or a scheduled task LegacyAppUpdater) writes these scrambled files to C:\Program Files\LegacyApp\config\ or C:\Users\Public\Updates\.
  • Filter/Exclusion: Exclude file paths under C:\Program Files\ or C:\Program Files (x86)\ for known legacy application directories (e.g., *LegacyApp*, *ERP*). If the detection is based on process execution, exclude processes named UpdateService.exe or those running under the SYSTEM or ServiceAccount context with a known parent process like svchost.exe or taskeng.exe.

• Scenario: Scheduled Data Archiving with Encryption/Scrambling