UnnamedScrambler21Beta211p0ke

Hunt Hypothesis

This detection identifies the execution of a specific obfuscated payload matching the “UnnamedScrambler21Beta211p0ke” YARA signature, which often indicates early-stage fileless or memory-resident malware activity designed to evade traditional signature-based defenses. Proactive hunting for this behavior in Azure Sentinel is critical because low-severity matches can represent initial reconnaissance phases of advanced threats that may escalate into significant compromises if not correlated with broader telemetry data.

YARA Rule

rule UnnamedScrambler21Beta211p0ke
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC B9 15 00 00 00 6A 00 6A 00 49 75 F9 53 56 57 B8 ?? 3A [2] E8 ?? EE FF FF 33 C0 55 68 ?? 43 [2] 64 FF 30 64 89 20 BA ?? 43 [2] B8 E4 64 [2] E8 0F FD FF FF 8B D8 85 DB 75 07 6A 00 E8 ?? EE FF FF BA E8 64 [2] 8B C3 8B 0D E4 64 [2] E8 ?? D7 FF FF B8 F8 [3] BA 04 00 00 00 E8 ?? EF FF FF 33 C0 A3 F8 [3] BB [4] C7 45 EC E8 64 [2] C7 45 E8 [4] C7 45 E4 [4] BE [4] BF [4] B8 E0 [3] BA 04 00 00 00 E8 ?? EF FF FF 68 F4 01 00 00 E8 ?? EE FF FF 83 7B 04 00 75 0B 83 3B 00 0F 86 ?? 07 00 00 EB 06 0F 8E ?? 07 00 00 8B 03 8B D0 B8 E4 [3] E8 ?? E5 FF FF B8 E4 [3] E8 ?? E3 FF FF 8B D0 8B 45 EC 8B 0B E8 }

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 UnnamedScrambler21Beta211p0ke detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Endpoint Protection Scans

  • Context: The YARA signature likely matches a specific byte pattern or string found in the scanning engine of major EDR solutions. When CrowdStrike Falcon, Microsoft Defender for Endpoint, or Carbon Black perform their scheduled hourly definition updates or real-time file scans, they may spawn processes that trigger this rule due to shared library dependencies or similar code signatures.
  • Suggested Filter: Exclude process executions where the parent process is falcon.sys, MsMpEng.exe, or cbengine.exe and the file path resides within the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\).

• Scenario: Scheduled Backup Agent Operations

  • Context: Enterprise backup agents like Veeam Transport Service, Rubrik, or Commvault often utilize compression algorithms that generate temporary files with binary structures mimicking the rule’s detection logic. During nightly backup windows, these agents read and write large datasets containing the specific pattern identified by UnnamedScrambler21Beta211p0ke.
  • Suggested Filter: Create an exclusion for processes running under the service accounts VeeamTransport, RubrikAgent, or CommServe where the execution time falls within the defined backup window (e.g., 01:00–05:00 local time).

• Scenario: Software Deployment and Patching Cycles

  • Context: During enterprise-wide patch management cycles, tools such as Microsoft SCCM (Configuration Manager), Ivanti Neurons, or PDQ Deploy extract installation packages.