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Automatic information enumeration - Credit Cards

Need​

Enhancement of credit card validation and security measures

Context​

  • Usage of Python 3 for scripting and general-purpose programming
  • Usage of Django for building web applications in Python

Description​

Non compliant code​

from django.http import HttpResponse
from django.views import View

class CreditCardView(View):
    def get(self, request, *args, **kwargs):
        card_number = request.GET.get('card_number')
        expiration_date = request.GET.get('expiration_date')
        security_code = request.GET.get('security_code')

        # Process the credit card information without validation
        # This is where the vulnerability lies
        process_credit_card(card_number, expiration_date, security_code)

        return HttpResponse('Credit card processed successfully')

def process_credit_card(card_number, expiration_date, security_code):
    # This function represents the processing of the credit card information
    # In a real-world scenario, this might involve communicating with a payment gateway or similar
    pass

The above code is a Django view that processes credit card information. The view retrieves the credit card number, expiration date, and security code from the GET parameters of the request and then processes the credit card information without any validation.

The vulnerability lies in the fact that the view does not validate the credit card information before processing it. This allows an attacker to automatically enumerate credit card information by sending a large number of requests with different credit card numbers, expiration dates, and security codes. Since the view does not validate the credit card information, all these requests will be processed, potentially leading to a breach of sensitive information.

Steps​

  • Introduce input validation for the credit card information. This should include checks for the card number, expiration date, and security code.
  • For the card number, implement a Luhn algorithm check to ensure it's a valid number.
  • For the expiration date, ensure it's a future date and in the correct format (MM/YY or MM/YYYY).
  • For the security code (CVV), ensure it's a 3 or 4 digit number, depending on the card type.
  • Consider using a secure, third-party service for handling credit card information to ensure compliance with Payment Card Industry Data Security Standard (PCI DSS).
  • Encrypt sensitive data like credit card information during transmission and at rest.
  • Implement rate limiting to prevent brute force attacks and automatic enumeration of credit card information.

Compliant code​

from django.http import HttpResponse
from django.views import View
from datetime import datetime
import re

class CreditCardView(View):
    def get(self, request, *args, **kwargs):
        card_number = request.GET.get('card_number')
        expiration_date = request.GET.get('expiration_date')
        security_code = request.GET.get('security_code')

        # Validate the credit card information before processing
        if not self.validate_credit_card(card_number, expiration_date, security_code):
            return HttpResponse('Invalid credit card information')

        # Process the credit card information
        process_credit_card(card_number, expiration_date, security_code)

        return HttpResponse('Credit card processed successfully')

    def validate_credit_card(self, card_number, expiration_date, security_code):
        # Validate card number using Luhn algorithm
        if not self.luhn_check(card_number):
            return False

        # Validate expiration date
        if not self.validate_expiration_date(expiration_date):
            return False

        # Validate security code
        if not self.validate_security_code(security_code):
            return False

        return True

    def luhn_check(self, card_number):
        def digits_of(n):
            return [int(d) for d in str(n)]
        digits = digits_of(card_number)
        odd_digits = digits[-1::-2]
        even_digits = digits[-2::-2]
        checksum = sum(odd_digits)
        for d in even_digits:
            checksum += sum(digits_of(d*2))
        return checksum % 10 == 0

    def validate_expiration_date(self, expiration_date):
        try:
            if datetime.strptime(expiration_date, '%m/%Y') <= datetime.now():
                return False
        except ValueError:
            return False
        return True

    def validate_security_code(self, security_code):
        if re.fullmatch(r'\\d{3,4}', security_code) is None:
            return False
        return True

def process_credit_card(card_number, expiration_date, security_code):
    # This function represents the processing of the credit card information
    # In a real-world scenario, this might involve communicating with a payment gateway or similar
    pass

The updated code introduces input validation for the credit card information. This includes checks for the card number, expiration date, and security code.

  • For the card number, a Luhn algorithm check is implemented to ensure it's a valid number. The luhn_check function calculates the checksum of the card number and returns True if it's valid, False otherwise.
  • For the expiration date, the validate_expiration_date function checks if it's a future date and in the correct format (MM/YYYY). If the date is in the past or in an incorrect format, the function returns False.
  • For the security code (CVV), the validate_security_code function checks if it's a 3 or 4 digit number. If the security code doesn't match this pattern, the function returns False.

If any of these checks fail, the validate_credit_card function returns False and the credit card information is not processed.

Please note that this code does not include measures for PCI DSS compliance, encryption of sensitive data, or rate limiting. These are important considerations for a production environment and should be implemented as well.

References​

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