JAMv211

Hunt Hypothesis

This YARA rule targets specific memory patterns or code artifacts associated with the JAMv211 signature, potentially indicating the presence of a low-severity malware variant or a known exploit kit component within host processes. Proactively hunting for this signature allows the SOC team to identify stealthy or early-stage intrusions that may not yet trigger high-fidelity alerts, ensuring timely containment of low-visibility threats in the Azure Sentinel environment.

YARA Rule

rule JAMv211
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 06 16 07 BE [2] 8B FE B9 [2] FD FA F3 2E A5 FB 06 BD [2] 55 CB }

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 legacy Java-based enterprise application (e.g., an internal HR portal or legacy ERP system) is deployed or updated via a standard MSI/EXE installer that bundles a JAR file with specific version strings or class structures matching the JAMv211 signature.
  • Filter/Exclusion: Exclude files located in standard application installation directories (e.g., C:\Program Files\LegacyHR\, C:\Program Files (x86)\InternalERP\) or exclude specific known-good SHA-256 hashes of the bundled JAR files.
• Scenario: A developer or DevOps engineer runs a local build or test environment using a Java-based tool (e.g., Maven, Gradle, or a custom Java wrapper script) that generates temporary JAR artifacts or loads specific classes during the compilation/testing phase, triggering the rule on the developer’s workstation or build agent.
  • Filter/Exclusion: Exclude processes or files originating from known build tools (e.g., mvn.exe, gradle.bat, java.exe when parent process is a build agent) or exclude paths within developer workspace directories (e.g., C:\Users\dev\projects\, D:\builds\).
• Scenario: A scheduled maintenance job runs a Java-based backup or log rotation utility (e.g., a custom Java script or a tool like logrotate with a Java wrapper) that creates or modifies JAR files in a temporary directory (%TEMP% or C:\Temp\) during execution.
  • Filter/Exclusion: Exclude files in temporary directories (C:\Temp\, %TEMP%, C:\Windows\Temp\) if the parent process is a known scheduled task or service (e.g., TaskScheduler.exe, svchost.exe with specific service name) and the file age