ExeShieldv27b

Hunt Hypothesis

This YARA rule targets specific executable characteristics associated with ExeShield, a tool commonly used by adversaries to pack or protect malicious binaries to evade static analysis. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify potentially obfuscated payloads early in the kill chain, reducing the time to detect stealthy malware that may have bypassed initial perimeter defenses.

YARA Rule

rule ExeShieldv27b
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 06 68 40 85 06 00 C3 9C 60 E8 02 00 00 00 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB 3F 90 40 00 87 DD 8B 85 E6 90 40 00 01 85 33 90 40 00 66 C7 85 30 90 40 00 90 90 01 85 DA 90 40 00 01 85 DE 90 40 00 01 85 E2 90 40 00 BB 7B 11 00 00 03 9D EA 90 40 }

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

• Antivirus Signature Update Service: The MsMpEng.exe (Microsoft Defender) or CCSvc.exe (CrowdStrike Falcon) processes often spawn short-lived child processes or handle temporary executable files during signature database synchronization. These operations can briefly match YARA patterns looking for packed or obfuscated code structures.

  • Filter/Exclusion: Exclude parent process names MsMpEng.exe, CCSvc.exe, or CrowdStrikeFalconSensor.exe when the target file path resides in C:\ProgramData\Microsoft\Windows Defender\ or C:\ProgramData\CrowdStrike\.

• Java Application Server Deployment: Enterprise applications running on JBoss, Tomcat, or WebLogic frequently deploy .jar files or native helper executables (e.g., java.exe spawning jpackage artifacts) into temporary directories like C:\Temp\ or C:\Users\Public\. These binaries may contain specific byte sequences or header structures that trigger generic “packed executable” or “unknown compiler” YARA rules.

  • Filter/Exclusion: Exclude files with extensions .jar, .war, or .ear and parent processes java.exe or jbossctl.exe located in standard application server directories (e.g., C:\Program Files\Apache Tomcat\, C:\jboss\).

• Visual Studio Code Extension Installation: When developers install or update extensions in VS Code, the code.exe process extracts native binaries (often Node.js addons or C++ helpers) into the user’s AppData folder (%APPDATA%\Code\User\globalStorage\). These small, dynamically linked executables often lack standard PE headers or use non-standard packing, triggering YARA rules designed to catch suspicious loaders.

  • Filter/Exclusion: Exclude parent process code.exe or Code.exe when