Need

Implementation of robust data validation and input sanitization mechanisms

Context

• Usage of Python 3 for building applications and scripts
• Usage of Django for building web applications

Description

Non compliant code

        from django.http import HttpResponse
from django.views.decorators.csrf import csrf_exempt

@csrf_exempt
def vulnerable_view(request):
    username = request.POST.get('username')
    password = request.POST.get('password')
    
    # some processing here

    return HttpResponse("Data processed successfully.")
        
        

The above Django view is vulnerable due to the lack of data validation on the server side. The 'username' and 'password' fields are directly taken from the POST request without any checks for special characters or control over the size of the fields.

- username = request.POST.get('username'): This line of code retrieves the 'username' field from the POST request. There are no checks for special characters or size of the field. An attacker can inject malicious scripts or use a very large username to cause a buffer overflow.

- password = request.POST.get('password'): Similar to the 'username', the 'password' field is also retrieved without any validation. This can lead to the same vulnerabilities as mentioned above.

- return HttpResponse("Data processed successfully."): This line sends a response back to the client. If an attacker has sent malicious data in the 'username' or 'password' fields, they would get this success message, encouraging further attacks.

The lack of data validation in this code can lead to several attack vectors, including script injection and buffer overflow attacks. It's important to always validate and sanitize user input on the server side to prevent such vulnerabilities.

Steps

• Implement server-side validation for all incoming data. This includes checking for special characters and controlling the size of the fields that can be sent to the server.
• Use Django's form or model form for data validation. These forms provide built-in validation for various data types and can be customized to suit your needs.
• Ensure that all fields are properly sanitized before they are processed. This can prevent attacks such as SQL injection or cross-site scripting (XSS).
• Consider using Django's built-in CSRF protection for all views. This can help prevent cross-site request forgery attacks.
• Implement error handling to ensure that the application can gracefully handle invalid or malicious data.
• Regularly update and patch your application to protect against known vulnerabilities.

Compliant code

        from django import forms
from django.http import HttpResponse
from django.views.decorators.csrf import csrf_protect
from django.core.exceptions import ValidationError

class UserForm(forms.Form):
    username = forms.CharField(max_length=100)
    password = forms.CharField(max_length=100)

@csrf_protect
def secure_view(request):
    if request.method == 'POST':
        form = UserForm(request.POST)
        if form.is_valid():
            username = form.cleaned_data['username']
            password = form.cleaned_data['password']
            
            # some processing here

            return HttpResponse("Data processed successfully.")
        else:
            raise ValidationError("Invalid data")
    else:
        form = UserForm()

    return render(request, 'form_template.html', {'form': form})
        
        

The above code fixes the vulnerability by implementing server-side validation for all incoming data.

1. Data Validation: A Django form UserForm is used to validate the incoming data. The form fields username and password are defined as CharFields with a maximum length of 100 characters. This controls the size of the fields that can be sent to the server. Django forms provide built-in validation for various data types and can be customized to suit your needs.

2. CSRF Protection: The view secure_view is decorated with @csrf_protect which enables Django's built-in CSRF protection for the view. This can help prevent cross-site request forgery attacks.

3. Error Handling: If the form is not valid, a ValidationError is raised. This ensures that the application can gracefully handle invalid or malicious data.

4. Data Sanitization: The form.cleaned_data dictionary contains the cleaned data that has been sanitized, validated and converted into Python-friendly types. This can prevent attacks such as SQL injection or cross-site scripting (XSS).

Remember to regularly update and patch your application to protect against known vulnerabilities.

References

• 186. Lack of data validation - Web Service