EXEStealthv272

Hunt Hypothesis

This rule targets the execution of potentially obfuscated or packed executables that may indicate stealthy malware deployment or fileless attack techniques. Proactively hunting for these indicators helps the SOC team identify low-fidelity threats that might evade standard signature-based detections, ensuring early visibility into suspicious binary activity within the Azure environment.

YARA Rule

rule EXEStealthv272
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 00 EB 2F 53 68 61 72 65 77 61 72 65 20 2D 20 }

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 dotnet.exe CLI tool during a standard .NET Core/5+ application build or publish process triggered by a CI/CD pipeline (e.g., Azure DevOps or GitHub Actions) on a build agent.
  • Filter/Exclusion: Exclude processes where the parent process is dotnet.exe, msbuild.exe, or vstest.console.exe, and the command line contains arguments like build, publish, or restore.
• Scenario: Running the kubectl command-line interface to deploy or manage Kubernetes workloads, where the binary is often distributed as a standalone executable that may match generic stealth or packing heuristics.
  • Filter/Exclusion: Exclude processes named kubectl.exe or kubectl where the parent process is a known shell (cmd.exe, powershell.exe, bash.exe) and the command line starts with kubectl followed by standard verbs like apply, get, delete, or create.
• Scenario: Execution of the terraform.exe binary during infrastructure-as-code provisioning tasks, which is frequently downloaded as a standalone binary and may exhibit characteristics that trigger generic EXE stealth detections.
  • Filter/Exclusion: Exclude processes named terraform.exe where the parent process is a shell or a CI/CD agent, and the command line contains standard Terraform commands such as plan, apply, init, or destroy.
• Scenario: Running the winget.exe (Windows Package Manager) tool to install or update software in a user session, which is a native Microsoft tool but may be flagged if its binary signature or path is not explicitly whitelisted in the YARA rule’s context.
  • Filter/Exclusion: Exclude processes named winget.exe where the path is under `C:\Program Files\