silent banker

Hunt Hypothesis

This detection identifies the Silent Banker malware behavior, which involves injecting malicious code into legitimate banking applications to intercept and manipulate financial transactions without triggering standard alerts. A SOC team should proactively hunt for this in Azure Sentinel because its stealthy nature allows adversaries to exfiltrate sensitive credentials and funds while remaining undetected by conventional perimeter defenses.

YARA Rule

rule silent_banker : banker
{
      meta:
		author="malware-lu"
    strings:
        $a = {6A 40 68 00 30 00 00 6A 14 8D 91}
        $b = {8D 4D B0 2B C1 83 C0 27 99 6A 4E 59 F7 F9}
        $c = "UVODFRYSIHLNWPEJXQZAKCBGMT"

    condition:
        $a or $b or $c
}

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 3 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Silent Banker detection rule, including suggested filters and exclusions tailored for a legitimate enterprise environment:

• Scenario: Automated Browser Profile Updates via Group Policy

  • Context: Enterprise IT administrators often use tools like Microsoft Endpoint Configuration Manager (MECM) or Intune to push silent updates to browser profiles (e.g., Chrome, Edge) during off-hours. These processes frequently launch msiexec.exe or the browser executable itself with specific command-line arguments that mimic the “silent” execution pattern of a banking trojan.
  • Suggested Filter: Exclude process executions where the parent process is ccmsetup.exe, intune-management-agent.exe, or gpupdate.exe, and the command line contains flags such as /quiet, /passive, or --no-first-run.

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Security suites like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint run scheduled jobs to download and install new definition packs. These agents often spawn child processes that execute silently in the background, which can trigger the YARA rule if they match specific binary signatures associated with banking security modules.
  • Suggested Filter: Create an exclusion for process trees where the root parent is C:\Program Files\CrowdStrike\fs_qrte.exe (or equivalent agent paths) and the execution occurs within a defined maintenance window (e.g., 02:00–04:00 local time).

• Scenario: Legacy ERP or CRM Client Auto-Refresh

  • Context: In financial enterprises, legacy clients for systems like SAP, Salesforce, or Oracle Financials often run background synchronization services. These services may launch a helper process (e.g.,