PESHiELDv01bMTE

Hunt Hypothesis

This YARA rule targets specific PE file characteristics associated with the PESHiELDv01bMTE signature, likely indicating the presence of a low-severity malware variant or a benign tool with suspicious structural anomalies. Proactively hunting for these indicators in Azure Sentinel allows the SOC team to identify dormant or stealthy threats that may evade standard behavioral detections, ensuring early visibility into potential low-fidelity compromises within the environment.

YARA Rule

rule PESHiELDv01bMTE
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [26] B9 1B 01 [2] D1 }

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

• Scenario: Execution of the Microsoft Defender Antivirus update service (MpCmdRun.exe) or the Windows Update client (wuauclt.exe) during a scheduled patch Tuesday cycle, where the executable binary contains specific version strings or resource sections that match the YARA pattern.
  • Filter/Exclusion: Exclude processes where the parent process is svchost.exe (specifically the wuauserv or dcomlaunch service group) and the file path resides in C:\Windows\System32\ or C:\Program Files\Windows Defender\.
• Scenario: Deployment of Sysinternals tools (e.g., procexp.exe, procmon.exe, or strings.exe) by a Tier 2 support engineer or a CI/CD pipeline agent for troubleshooting or code analysis, where the tool’s embedded metadata or specific code blocks trigger the signature.
  • Filter/Exclusion: Allowlist specific executable names (procexp.exe, procmon.exe, strings.exe) when executed by service accounts (e.g., svc_ci_cd, svc_support) or from designated tool directories (e.g., C:\Tools\Sysinternals\, C:\CI\Agents\).
• Scenario: Execution of Java Runtime Environment (JRE) or .NET Framework host processes (java.exe, dotnet.exe, mscorwks.exe) running custom enterprise applications or middleware, where the JIT-compiled code or specific library references match the YARA rule’s byte patterns.
  • Filter/Exclusion: Exclude processes with names java.exe, dotnet.exe, or mscorwks.exe when the working directory or command line arguments indicate a known application path (e.g., C:\Apps\ERP\, C:\Services\Middleware\) and