VxPhoenix927

Hunt Hypothesis

This hypothesis targets the execution of the VxPhoenix927 malware variant, which may indicate an adversary attempting to establish a foothold or perform initial access activities within the environment. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify low-severity threats that might otherwise evade broader behavioral detections, ensuring timely containment of known malicious payloads.

YARA Rule

rule VxPhoenix927
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 5E 81 C6 [2] BF 00 01 B9 04 00 F3 A4 E8 }

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 application server (e.g., Tomcat or WildFly) running a specific version of the java.util.zip library or a third-party compression utility that uses a non-standard internal header structure matching the VxPhoenix927 signature.
  • Filter/Exclusion: Exclude files located in the application server’s lib/ or plugins/ directories (e.g., C:\Program Files\Apache Tomcat 9\lib\*.jar) where the file extension is .jar or .war, and the parent process is a known Java runtime (java.exe, javaw.exe).
• Scenario: A developer or DevOps engineer using a specialized binary patching tool (such as HxD, 010 Editor, or a custom Python script using lief) to modify a PE executable in a staging environment, creating a temporary file that retains the original section layout but with modified headers that trigger the YARA rule.
  • Filter/Exclusion: Exclude files in common temporary or build directories (e.g., C:\Users\<User>\AppData\Local\Temp\, C:\builds\, C:\workspace\) where the file was created within the last 15 minutes and the parent process is an editor or build tool (hxd.exe, python.exe, msbuild.exe).
• Scenario: An automated backup or deduplication agent (such as Veeam, Commvault, or Rubrik) creating a temporary deduplicated chunk file or a compressed archive segment that coincidentally matches the byte pattern defined in the VxPhoenix927 rule, particularly if the rule targets specific magic bytes or section names.
  • Filter/Exclusion: Exclude files with extensions .vbk, .vib, .ckp, or .dedup located