EXEStealthv274

Hunt Hypothesis

This YARA rule targets specific executable file characteristics associated with the EXEStealth malware family, which often employs stealthy packing or obfuscation techniques to evade standard signature-based detection. Proactively hunting for these indicators in Azure Sentinel allows the SOC to identify potentially compromised endpoints or malicious artifacts before they execute lateral movement or establish persistence within the environment.

YARA Rule

rule EXEStealthv274
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 00 EB 17 53 68 61 72 65 77 61 72 65 20 2D 20 45 78 65 53 74 65 61 6C 74 68 00 60 90 E8 00 00 00 00 5D 81 ED C4 27 40 00 B9 15 00 00 00 83 C1 04 83 C1 01 EB 05 EB FE 83 C7 56 EB 00 83 E9 02 81 C1 78 43 27 65 EB 00 81 C1 10 25 94 00 81 E9 63 85 00 00 B9 }

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

• Legitimate Software Installation via Silent Installers: Many enterprise applications (e.g., Adobe Creative Cloud, Microsoft Office, or Oracle Java) use silent installers that drop temporary executable files in %TEMP% or %LOCALAPPDATA% which may match generic stealth patterns.
  • Filter/Exclusion: Exclude paths like C:\Users\*\AppData\Local\Temp\ and C:\ProgramData\Package Cache\ where the parent process is a known installer service (e.g., msiexec.exe, setup.exe, or install.exe).
• Java Runtime Environment (JRE) Temporary Executables: Java applications often create temporary .exe wrappers or launchers in the user’s temp directory to execute JAR files or native libraries, which can appear as suspicious standalone executables.
  • Filter/Exclusion: Exclude files located in C:\Users\*\AppData\Local\Temp\ if the parent process is java.exe, javaw.exe, or jrebin\javaw.exe.
• Development Environment Build Artifacts: Developers using tools like Visual Studio, IntelliJ, or Maven/Gradle may generate temporary executable artifacts or test binaries in project build directories (e.g., bin\, obj\, target\) that are not yet signed or registered in the software inventory.
  • Filter/Exclusion: Exclude paths containing \bin\, \obj\, \target\, or \build\ if the parent process is a known IDE or build tool (e.g., devenv.exe, idea64.exe, mvn.cmd, gradle.bat).
• Scheduled Task Maintenance Scripts: IT operations teams often deploy PowerShell or VBScript wrappers that spawn temporary executables for patching, log rotation, or database maintenance, which may be placed in `