Search strings and procedure in HelloWorld ATM Malware

Hunt Hypothesis

The detection identifies potential HelloWorld ATM malware by searching for suspicious strings and procedural patterns commonly associated with this specific malware variant. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect early-stage compromises and prevent financial loss from ATM malware infections.

YARA Rule

rule ATM_HelloWorld : malware
{
    meta:
        description = "Search strings and procedure in HelloWorld ATM Malware"
        author = "[email protected]"
        date = "2019-01-13"

    strings:
        $api1 = "CscCngOpen" ascii wide
        $api2 = "CscCngClose" ascii wide
        $string1 = "%d,%02d;" ascii wide
        $string2 = "MAX_NOTES" ascii wide
        $hex_var1 = { FF 15 ?? ?? ?? ?? BF 00 80 00 00 85 C7 }

    condition:
        (uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550) and all of them
}

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 5 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Legitimate scheduled job using “HelloWorld” in script name
  Description: A system administrator schedules a PowerShell script named HelloWorld.ps1 to perform routine system checks.
  Filter/Exclusion: Exclude processes where the script name contains “HelloWorld” and the process is associated with a known administrative task (e.g., schtasks.exe or powershell.exe with a known job ID).

• Scenario: Debugging session with “HelloWorld” in log output
  Description: A developer is testing a logging mechanism and includes “HelloWorld” as a test string in a log file or console output.
  Filter/Exclusion: Exclude processes where the parent process is a development tool (e.g., VisualStudio.exe, debugger.exe) or the output is directed to a known log file used for testing.

• Scenario: System update or patching using a script named “HelloWorld.bat”
  Description: An IT team uses a batch script named HelloWorld.bat to run a system update or patching task.
  Filter/Exclusion: Exclude processes where the script is executed by a known patching tool (e.g., WindowsUpdate.exe, msiexec.exe) or the script is located in a known system directory (e.g., C:\Windows\System32).

• Scenario: Admin task using “HelloWorld” in a custom script for monitoring
  Description: An admin creates a custom script named HelloWorld.ps1 to monitor system performance or service status.
  Filter/Exclusion: Exclude processes where the script is executed by a service or task scheduler (e.g., TaskScheduler.exe) and the script is located in a known admin script directory (e.g., C:\AdminScripts).

• **Scenario: Log file rotation or cleanup using “HelloWorld