credit card regex

Hunt Hypothesis

The detection rule identifies potential credit card numbers using a regex pattern, which may indicate an adversary attempting to exfiltrate or manipulate financial data. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect early signs of data breaches or credential stuffing attacks involving card information.

YARA Rule

rule credit_card_regex {
    strings: $ = "RegExp(\"[0-9]{13,16}\")"
    condition: any 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
• Source Rule

False Positive Guidance

• Scenario: A system administrator is manually entering a credit card number into a ticketing system for a test payment.
  Filter/Exclusion: Exclude entries made by users with the role “System Admin” or filter by the ticketing system (e.g., Jira, ServiceNow) and specific ticket IDs used for testing.

• Scenario: A scheduled job runs to generate reports and includes a placeholder credit card number for demonstration purposes.
  Filter/Exclusion: Exclude logs from the job name “Monthly_Report_Generator” or filter by the specific script path used for report generation.

• Scenario: A developer is testing a payment gateway integration and inputs a sample credit card number into a local development environment.
  Filter/Exclusion: Exclude logs from the local development machine (e.g., IP address 192.168.1.100) or filter by the application name “PaymentGatewayDevTool”.

• Scenario: A user is using a password manager that stores credit card information and the tool occasionally logs the data for debugging.
  Filter/Exclusion: Exclude logs from the password manager application (e.g., Bitwarden, 1Password) or filter by the specific log source or process name.

• Scenario: A customer service representative is using a CRM tool that auto-fills credit card information for a legitimate transaction.
  Filter/Exclusion: Exclude logs from the CRM system (e.g., Salesforce, Zendesk) or filter by the user role “CustomerServiceRep” and specific transaction IDs.