Might be PE Virus

Hunt Hypothesis

This rule identifies potential Portable Executable (PE) files that may be infected with malware, indicating an adversary has successfully delivered a malicious binary to a host. Proactively hunting for these detections allows the SOC team to isolate compromised endpoints early in the kill chain, preventing the execution of malicious code and subsequent lateral movement within the Azure environment.

YARA Rule

rule IsSuspicious
{
	meta:
		author="_pusher_"
		date = "2016-07"
		description="Might be PE Virus"
	condition:
		uint32(0x20) == 0x20202020	
}

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
• Source Rule

False Positive Guidance

• Scenario: A DevOps engineer uses dotnet build or msbuild to compile a C# application in a development environment, where the compiler generates a temporary .exe or .dll file that is immediately loaded into memory or executed for testing before being cleaned up.
  • Filter/Exclusion: Exclude processes where the parent process is MSBuild.exe, dotnet.exe, or csc.exe (C# Compiler), and the file path contains standard build directories like bin\Debug, bin\Release, or obj\.
• Scenario: An IT administrator runs a scheduled task using PowerShell to execute a small, self-contained .NET utility (e.g., a custom log rotation script or disk cleanup tool) that is stored in a standard administrative folder like C:\AdminTools\ or C:\Scripts\.
  • Filter/Exclusion: Exclude PE files located in known administrative script directories (e.g., C:\AdminTools\, C:\Scripts\, C:\ProgramData\CorpTools\) if the parent process is powershell.exe or pwsh.exe and the file size is below a certain threshold (e.g., < 500KB).
• Scenario: A developer installs a new NuGet package or Python pip package that includes native C/C++ extensions compiled into .dll or .pyd files, which are then loaded by the application runtime (e.g., python.exe or node.exe).
  • Filter/Exclusion: Exclude PE files in package cache directories such as C:\Users\<User>\.nuget\packages\, C:\Users\<User>\.cache\pip\, or node_modules\ if the parent process is a known runtime interpreter (python.exe, node.exe, java.exe).