VxSpanz

Hunt Hypothesis

This detection identifies the presence of VxSpanz, a YARA signature associated with specific malicious payloads or exploit kits, indicating potential compromise or staging activity within the environment. Proactively hunting for this signature allows the SOC team to uncover low-severity threats that may evade traditional behavioral detections, ensuring early identification of known malicious artifacts before they progress to more impactful stages of the attack lifecycle.

YARA Rule

rule VxSpanz
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 5E 81 EE [2] 8D 94 [2] B4 1A CD 21 C7 84 }

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

Here are specific false positive scenarios for the YARA rule VxSpanz (commonly associated with detecting specific variants of ransomware or trojans, often involving memory scanning or specific string patterns), along with suggested filters:

• Legitimate Memory Scanning by EDR/Antivirus Tools: Tools like CrowdStrike Falcon, Carbon Black, or Microsoft Defender for Endpoint frequently perform deep memory scans to detect fileless malware. These scans can temporarily load or mimic the byte patterns targeted by VxSpanz, especially if the rule looks for specific API hooking strings or memory layout signatures.

  • Filter/Exclusion: Exclude processes where the parent is a known EDR agent (e.g., FalconSensor.exe, Cb.exe, MsMpEng.exe) and the action is MemoryRead or ProcessScan. Alternatively, exclude if the process is running in a protected service context with high integrity.

• Java Virtual Machine (JVM) Garbage Collection and Class Loading: Enterprise applications heavily reliant on Java (e.g., Oracle WebLogic, Tomcat, Spring Boot services) may trigger YARA rules that look for generic code patterns or specific string sequences in memory. The JVM’s class loader and garbage collector can create transient memory states that match broad YARA patterns, particularly if the rule includes generic strings like java.lang or common library names.

  • Filter/Exclusion: Exclude processes matching java.exe or jvm.dll when the working directory is within a known application server path (e.g., C:\Program Files\Apache Tomcat\, C:\Oracle\Middleware\). Add a condition to ignore matches if the process has been running for >5 minutes and has no child processes.

• Scheduled Backup and Deduplication Jobs: Backup software like Veeam Backup & Replication,