MSLRHv032afakeBJFNT13emadicius

Hunt Hypothesis

This rule targets a specific YARA signature that likely identifies a known malware family or suspicious code pattern, potentially indicating the presence of a low-severity threat such as a web shell, script-based payload, or minor variant of a common malware strain. Proactively hunting for this signature in Azure Sentinel allows the SOC team to detect early-stage infections or dormant threats that may not yet trigger higher-severity alerts, enabling faster containment and reducing the risk of lateral movement or data exfiltration.

YARA Rule

rule MSLRHv032afakeBJFNT13emadicius
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 03 3A 4D 3A 1E EB 02 CD 20 9C EB 02 CD 20 EB 02 CD 20 60 EB 02 C7 05 EB 02 CD 20 E8 03 00 00 00 E9 EB 04 58 40 50 C3 61 9D 1F 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 }

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 a legitimate cross-platform build tool like CMake or Ninja to compile C/C++ source code on a Windows build agent. The YARA rule likely matches the specific binary structure or string patterns of the generated executables or intermediate object files, which can resemble the target malware’s packing or obfuscation techniques.
  • Filter/Exclusion: Exclude files located in standard build directories (e.g., C:\Builds\, C:\Jenkins\workspace\) or exclude processes where the parent process is cmake.exe, ninja.exe, or msbuild.exe.
• Scenario: An administrator performs a routine patching or deployment task using Ansible or Chef to push configuration scripts or small utility binaries to remote servers. The rule may trigger on the temporary .tmp files created during the transfer or execution of these scripts, especially if they are signed by a generic CA or lack a specific enterprise signature.
  • Filter/Exclusion: Exclude files with extensions .tmp, .ps1, or .bat that are located in C:\Windows\Temp\ or C:\Users\<User>\AppData\Local\Temp\ and were created within the last 15 minutes.
• Scenario: A security team runs a VirusTotal or CrowdStrike Falcon quick scan on a newly downloaded ISO image or installer package (e.g., setup.exe for a new application like Zoom or Slack). The YARA rule may match the specific version string or resource section of the installer, which coincidentally overlaps with the malware’s fingerprint.
  • Filter/Exclusion: Exclude files that are part of a known application install directory (e.g., C:\Program Files\Zoom\, `C:\Program Files\