Lack of data validation - Emails

Need

Implementation of email address validation to prevent registration with disposable mailboxes

Context

• Usage of Python 3 for writing and executing Python code
• Usage of Django for building web applications in Python

Description

Non compliant code

from django.contrib.auth.models import User
from django.http import JsonResponse

def register(request):
    email = request.POST.get('email')
    password = request.POST.get('password')
    
    user = User.objects.create_user(email, password)
    user.save()
    
    return JsonResponse({"message": "User registered successfully."})

In the above code, the register view takes a POST request and extracts the 'email' and 'password' from the request. It then creates a new user using Django's built-in User model and saves it to the database.

The vulnerability here is that there is no validation performed on the 'email' before it is used to create a new user. This means that an attacker could use a disposable email address (such as one provided by YOPMail) to register multiple accounts, potentially leading to spamming, rate limit evasion, or other forms of abuse.

Without proper validation, the application also risks storing and processing potentially invalid or harmful data, which could lead to further vulnerabilities.

Here's how this vulnerability could be exploited:

1. An attacker identifies that the application does not perform email validation during registration.
2. The attacker uses a disposable email service to generate a large number of email addresses.
3. The attacker uses these email addresses to register multiple accounts on the application.
4. The attacker uses these accounts for malicious activities, such as spamming other users, evading rate limits, or exploiting other vulnerabilities in the application.

The lack of validation also poses a risk to the application's data integrity, as it allows the creation of users with invalid email addresses. This could lead to issues with email delivery, user management, and other functions that rely on users' email addresses.

Steps

• Import a library to validate the email domain.
• Create a list of disposable email domains that you want to block.
• Before creating the user, validate the email domain against the list of blocked domains.
• If the email domain is in the blocked list, return an error message.
• If the email domain is not in the blocked list, proceed with the user creation.

Compliant code

from django.contrib.auth.models import User
from django.http import JsonResponse
from validate_email_address import validate_email

def register(request):
    email = request.POST.get('email')
    password = request.POST.get('password')
    
    # List of disposable email domains
    blocked_domains = ['yopmail.com', 'tempmail.com', '10minutemail.com']
    
    # Validate the email domain
    email_domain = email.split('@')[-1]
    if email_domain in blocked_domains:
        return JsonResponse({"error": "Registration with disposable email addresses is not allowed."}, status=400)
    
    if not validate_email(email):
        return JsonResponse({"error": "Invalid email address."}, status=400)
    
    user = User.objects.create_user(email, password)
    user.save()
    
    return JsonResponse({"message": "User registered successfully."})

The updated code now includes a validation step before creating a new user. This validation step checks if the email provided by the user is from a disposable email service or if it's invalid.

First, we import a library called validate_email_address which will be used to check if the email address is valid.

Next, we create a list of disposable email domains that we want to block. This list can be updated as needed.

In the registration function, before creating the user, we split the email address at the '@' symbol and take the last part which is the domain of the email. We then check if this domain is in our list of blocked domains. If it is, we return an error message and a 400 status code to indicate a bad request.

We also use the validate_email function from the validate_email_address library to check if the email address is valid. If it's not, we return an error message and a 400 status code.

If the email domain is not in the blocked list and the email is valid, we proceed with the user creation as before.

References

• 199.Lack of data validation - Emails