VxEddie1028

Hunt Hypothesis

This YARA rule targets specific memory patterns associated with the VxEddie1028 malware family, indicating potential in-memory execution or obfuscated code injection. Proactively hunting for this signature allows the SOC to identify low-severity, stealthy threats that may evade traditional network-based detections by scanning for known malicious code structures within host telemetry.

YARA Rule

rule VxEddie1028
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [2] 5E FC 83 [2] 81 [3] 4D 5A [2] FA 8B E6 81 C4 [2] FB 3B [5] 50 06 56 1E B8 FE 4B CD 21 81 FF BB 55 [2] 07 [3] 07 B4 49 CD 21 BB FF FF B4 48 CD 21 }

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 custom Python script or a lightweight C# utility to perform in-memory string manipulation or data obfuscation for a local API test. The script loads a small, unsigned DLL or executable that contains specific byte sequences matching the VxEddie1028 signature, triggering the alert during a routine dotnet run or python main.py execution.

  • Filter/Exclusion: Exclude processes where the parent process is python.exe, dotnet.exe, or node.exe and the file path resides within a known development directory (e.g., C:\Users\<user>\Projects\ or C:\dev\). Additionally, allowlist specific hash values of the test binaries if they are version-controlled.

• Scenario: An IT administrator runs a legacy backup verification tool (e.g., a custom wrapper for Veeam or Acronis) that uses a small, statically linked C++ helper binary to validate checksums. This helper binary is not digitally signed by a major vendor and contains a specific code pattern that matches the YARA rule, causing a false positive during the nightly scheduled backup job.

  • Filter/Exclusion: Exclude alerts where the process name matches the specific backup helper (e.g., verify_checksums.exe) and the parent process is the main backup service (e.g., VeeamBackupSvc.exe or AcronisService.exe). Ensure the exclusion is scoped to the specific service account used for backups (e.g., DOMAIN\svc-backup).

• Scenario: A security engineer performs a manual test of a new endpoint detection agent by executing a small, unsigned test harness executable designed to mimic specific memory layouts. This test executable is placed in a temporary directory and executed via cmd.exe to verify logging, triggering the rule due to its unique binary structure.