EXEStealthv27

Hunt Hypothesis

This rule detects the presence of the EXEStealth malware family, a known threat actor tool often used for initial access and lateral movement within enterprise networks. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify compromised endpoints early, preventing the malware from establishing persistence or escalating privileges before traditional behavioral detections trigger.

YARA Rule

rule EXEStealthv27
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 00 60 EB 00 E8 00 00 00 00 5D 81 ED D3 26 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

• Scenario: Execution of the Sysinternals PsExec utility by a system administrator to perform remote service management or file transfer. The binary often contains specific string patterns or section headers that match the EXEStealthv27 heuristic, especially if it is a custom-compiled or older version.

  • Filter/Exclusion: Exclude processes where the parent process is services.exe or svchost.exe and the command line contains PsExec.exe with arguments like -s (system) or -accepteula. Alternatively, whitelist the specific SHA256 hash of the known-good PsExec binary used in the environment.

• Scenario: Execution of VMware Tools (vmtoolsd.exe or vmware-toolbox-cmd.exe) during automated guest OS provisioning or snapshot operations. These utilities frequently interact with low-level system resources and may exhibit stealth-like characteristics in their PE structure or string tables that trigger the YARA rule.

  • Filter/Exclusion: Exclude processes running from the standard VMware Tools installation path (e.g., C:\Program Files\VMware\VMware Tools\) where the parent process is vmtoolsd.exe or vmware-usbarbitrator64.exe.

• Scenario: Execution of Microsoft Defender for Endpoint or CrowdStrike Falcon sensor components during real-time scanning or policy updates. Security agents often use packed or obfuscated modules to avoid detection by other AVs, which can cause false positives in heuristic YARA rules like EXEStealthv27.

  • Filter/Exclusion: Exclude processes where the parent process is the security agent’s main service (e.g., MsMpEng.exe for Defender or FalconSensor.exe for CrowdStrike) and the executable path resides within the vendor’s installation directory (e