VxTrojanTelefoon

Hunt Hypothesis

This detection identifies the presence of the Telefoon Trojan, a banking malware variant that targets financial credentials and communication channels on endpoints within the Azure Sentinel environment. Proactive hunting for this threat is essential to uncover early-stage infections before they escalate into data exfiltration or lateral movement attacks, ensuring robust protection for sensitive organizational assets.

YARA Rule

rule VxTrojanTelefoon
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 1E E8 3B 01 BF CC 01 2E 03 3E CA 01 2E C7 05 }

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 4 specific false positive scenarios for the VxTrojanTelefoon detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Backup Agent Execution

  • Context: Enterprise backup solutions like Veeam Backup & Replication or Rubrik often spawn child processes to handle data transfer. These agents frequently utilize network sockets and memory manipulation techniques that mimic the behavior of a telecom-focused trojan, triggering the YARA signature on the vbrservice.exe or rubrik-agent.exe process.
  • Suggested Filter: Create an exclusion based on the parent process image path. Exclude alerts where the parent process is located in C:\Program Files\Veeam\Backup and Replication\ or C:\Rubrik\rubrik-agent\.

• Scenario: Scheduled Endpoint Protection Scans

  • Context: During off-hours, CrowdStrike Falcon or Microsoft Defender for Endpoint performs scheduled deep scans. The scanning engine (FalconService.exe or MsMpEng.exe) may load specific DLLs related to network telephony modules (e.g., VoIP integration plugins) which match the YARA pattern’s memory signatures.
  • Suggested Filter: Implement a time-based exclusion window for these processes between 01:00 and 05:00 local time, or exclude specific file hashes known to belong to the vendor’s update packages (e.g., falcon-sensor-update.exe).

• Scenario: Unified Communications Client Updates

  • Context: Legitimate business communication tools such as Microsoft Teams, Zoom Workplace, or Cisco Webex frequently run background updater services (TeamsUpdate.exe, ZoomUpdater.exe) that establish persistent network connections and inject code into the main client process. This behavior often overlaps with the ”