kkrunchy023alpha2Ryd

Hunt Hypothesis

This YARA rule targets a specific low-severity signature, likely indicating the presence of a known benign or low-risk artifact, such as a common software component or a minor malware variant, within the environment. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to establish a baseline for this specific indicator, ensuring that any unexpected occurrences or context-dependent anomalies can be quickly triaged to distinguish between routine noise and potential early-stage compromise.

YARA Rule

rule kkrunchy023alpha2Ryd
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BD [4] C7 45 00 [3] 00 B8 [3] 00 89 45 04 89 45 54 50 C7 45 10 [3] 00 FF 4D 0C FF 45 14 FF 45 58 C6 45 1C 08 B8 00 08 00 00 8D 7D 30 AB AB AB AB BB 00 00 D8 00 BF }
	$a1 = { BD [4] C7 45 00 [3] 00 B8 [3] 00 89 45 04 89 45 54 50 C7 45 10 [3] 00 FF 4D 0C FF 45 14 FF 45 58 C6 45 1C 08 B8 00 08 00 00 8D 7D 30 AB AB AB AB BB 00 00 D8 00 BF [3] 01 31 C9 41 8D 74 09 01 B8 CA 8E 2A 2E 99 F7 F6 01 C3 89 D8 C1 E8 15 AB FE C1 75 E8 BE }

condition:
		$a0 at pe.entry_point or $a1 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Legacy .NET Application Compilation: A developer or build server compiles a custom internal tool using the csc.exe (C# Compiler) or vbc.exe (VB.NET Compiler) that embeds specific string constants or version metadata matching the YARA signature. This is common in CI/CD pipelines where intermediate assembly files are generated in temporary directories.
  • Filter/Exclusion: Exclude processes where the parent process is MSBuild.exe, dotnet.exe, or csc.exe, and the file path contains \bin\ or \obj\ directories.
• Java Development Kit (JDK) Tooling: The javac.exe compiler or jar.exe tool creates temporary class files or JAR archives that contain specific bytecode patterns or manifest entries triggering the rule. This often occurs during local development or automated unit test execution.
  • Filter/Exclusion: Exclude files located in standard Java workspace directories such as \target\classes\, \build\, or \tmp\ when the parent process is javac.exe, java.exe, or gradle.exe.
• Python Packaging and Wheel Creation: The pip.exe or wheel.exe tools generate .whl files or temporary build artifacts that may contain specific binary structures or metadata strings matching the detection logic. This is frequent in data science environments or Python-based microservice deployments.
  • Filter/Exclusion: Exclude files with extensions .whl, .egg, or .pyc located in ~/.cache/pip/, C:\Python*\Lib\site-packages\, or temporary build directories when the parent process is pip.exe or python.exe.
• Go Language Binary Compilation: The go.exe build tool generates executable binaries that may embed specific build flags, module paths, or linker directives that align with the Y