MSLRHv032afakeWWPack321xemadicius

Hunt Hypothesis

This YARA rule targets a specific memory or file pattern associated with the “fakeWWPack” component, likely indicating the presence of a low-severity web-based payload or packing mechanism used for initial access or obfuscation. Proactively hunting for this signature allows the SOC team to identify dormant or stealthy artifacts in Azure Sentinel that may not trigger standard behavioral alerts, ensuring early detection of targeted web infrastructure compromises.

YARA Rule

rule MSLRHv032afakeWWPack321xemadicius
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 53 55 8B E8 33 DB EB 60 0D 0A 0D 0A 57 57 50 61 63 6B 33 32 20 64 65 63 6F 6D 70 72 65 73 73 69 6F 6E 20 72 6F 75 74 69 6E 65 20 76 65 72 73 69 6F 6E 20 31 2E 31 32 0D 0A 28 63 29 20 31 39 39 38 20 50 69 6F 74 72 20 57 61 72 65 7A 61 6B 20 61 6E 64 20 52 61 66 61 6C 20 57 69 65 72 7A 62 69 63 6B 69 0D 0A 0D 0A 5D 5B 90 EB 05 E8 EB 04 40 00 EB FA E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 74 04 75 02 EB 02 EB 01 81 50 E8 02 00 00 00 29 5A 58 6B C0 03 E8 02 00 00 00 29 5A 83 C4 04 58 74 04 75 02 EB 02 EB 01 81 0F 31 50 0F 31 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF }

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 sysadmin uses a custom Python or PowerShell script to generate a self-contained executable (e.g., via PyInstaller or Nuitka) that bundles specific C library headers or static libraries matching the YARA signature. This is common in CI/CD pipelines where build artifacts are scanned before deployment.

  • Filter/Exclusion: Exclude files located in standard build artifact directories (e.g., C:\Builds\, D:\Artifacts\, or *.tmp extensions) or exclude processes originating from known build tools like dotnet.exe, msbuild.exe, or python.exe when the file path contains dist/, build/, or out/.

• Scenario: An enterprise endpoint protection agent (such as CrowdStrike Falcon, Carbon Black, or SentinelOne) performs a real-time scan of a newly downloaded installer package (e.g., setup.msi or install.exe) that contains embedded resources or version strings matching the rule’s byte pattern. This often happens during mass software deployments via SCCM or Intune.

  • Filter/Exclusion: Exclude events where the parent process is a known deployment engine (e.g., ccmsetup.exe, msiexec.exe, intunewua.exe, or ccmexec.exe) and the file extension is .msi, .msp, or .exe within the C:\Windows\Installer\ or C:\ProgramData\ paths.

• Scenario: A legitimate Java or .NET application (e.g., a custom internal line-of-business tool) loads a native DLL or JAR file that includes a specific version string, comment, or resource block matching the YARA rule. This can occur when the application is updated and the new binary is cached in the user’s %LOCALAPPDATA% or %TEMP% directory. *