ExeBundlev30standardloader

Hunt Hypothesis

This rule detects the presence of a standard loader component within an executable bundle, a technique often used by adversaries to obfuscate malicious payloads and facilitate initial access or persistence. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify potentially compromised endpoints or staging areas before the loader executes its intended payload, reducing the risk of undetected lateral movement or privilege escalation.

YARA Rule

rule ExeBundlev30standardloader
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 00 00 00 00 60 BE 00 B0 42 00 8D BE 00 60 FD FF C7 87 B0 E4 02 00 31 3C 4B DF 57 83 CD FF EB 0E 90 90 90 90 8A 06 46 88 07 47 01 DB 75 07 8B 1E 83 EE FC 11 DB 72 ED B8 01 00 00 00 01 DB }

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: A developer or DevOps engineer uses 7-Zip or WinRAR to extract a large software bundle (e.g., a .NET SDK or Java JRE) directly to a temporary directory (%TEMP% or %LOCALAPPDATA%\Temp). The extracted executable files often retain the original archive’s metadata or have a packed structure that matches the “standard loader” heuristic, especially if the extraction tool itself is a 32-bit application running on a 64-bit OS.

  • Filter/Exclusion: Exclude paths containing \Temp\, \Tmp\, or %LOCALAPPDATA%\Temp\ where the parent process is a known archiver (e.g., 7z.exe, WinRAR.exe, tar.exe). Alternatively, exclude if the file extension is .dll or .exe and the parent process is in the whitelist of archiving tools.

• Scenario: An IT administrator runs Chocolatey or Winget to install or update enterprise software (e.g., choco install vscode or winget install Microsoft.VisualStudioCode). These package managers often download and execute installers from temporary cache directories, and the installer binaries may be bundled or packed in a way that triggers the “ExeBundle” signature, particularly if the installer is a self-extracting archive.

  • Filter/Exclusion: Exclude if the parent process is choco.exe, winget.exe, or msiexec.exe and the file path contains \Chocolatey\ or \Packages\. Additionally, exclude if the command line arguments contain /i (install) or --install and the process name matches known package manager executables.

• Scenario: A scheduled task or service update for Java (JRE/JDK) or .NET Framework runs a background updater (e.g., `jav