USSR031bySpirit

Hunt Hypothesis

This rule detects the presence of the “USSR031bySpirit” YARA signature, which typically identifies specific malicious payloads or memory artifacts associated with targeted espionage or backdoor implants. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify dormant or low-noise threats that may have evaded traditional endpoint detections, ensuring early containment of sophisticated adversary footholds within the environment.

YARA Rule

rule USSR031bySpirit
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 00 00 5D 83 C5 12 55 C3 20 83 B8 ED 20 37 EF C6 B9 79 37 9E 8C C9 30 C9 E3 01 C3 BE 32 [3] B0 ?? 30 06 8A 06 46 81 FE 00 [3] 7C F3 }

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

• Legacy Application Deployment via Group Policy: When IT administrators deploy legacy line-of-business applications (e.g., older versions of Adobe Acrobat, Java Runtime, or specific banking plugins) via Group Policy Object (GPO) software installation, the installer executables or associated DLLs may match the USSR031bySpirit signature due to specific memory layout or string patterns common in older binaries.

  • Filter/Exclusion: Exclude files located in C:\Program Files\ or C:\Program Files (x86)\ where the parent process is gpupdate.exe or svchost.exe (specifically the gpupdate service context), or exclude specific known installer paths like C:\Windows\Installer\ during GPO refresh cycles.

• Antivirus/EDR Self-Update and Scan Operations: During full system scans or real-time protection updates, security products like CrowdStrike Falcon, Microsoft Defender for Endpoint, or Sophos may load specific driver modules or scan engines that exhibit byte patterns matching this YARA rule. This often occurs when the security agent is inspecting its own binary or loading a new definition pack.

  • Filter/Exclusion: Exclude processes where the parent process is the security agent’s main service (e.g., FalconService.exe, MsMpEng.exe, Sophos64.exe) and the file path resides in the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\, C:\Program Files\Microsoft Security Client\).

• Scheduled Database Maintenance Jobs: Database management systems like SQL Server or Oracle often run scheduled maintenance jobs (e.g., sqlagent.exe executing DBCC CHECKDB or backup routines) that load specific native libraries or execute stored procedures compiled to native code. These operations can generate memory or file artifacts that trigger the `USSR031by