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Restricted fields manipulation

Need​

Prevention of unauthorized access and manipulation of restricted fields in employee registration functionality

Context​

  • Usage of Python 3.0+ for developing Python applications
  • Usage of Django for building web applications in Python

Description​

Non compliant code​

from django.shortcuts import render
from django.views.decorators.csrf import csrf_exempt
from .models import Employee

@csrf_exempt
def update_employee(request):
    if request.method == 'POST':
        employee_id = request.POST.get('employee_id')
        dni = request.POST.get('dni')
        name = request.POST.get('name')
        email = request.POST.get('email')
        dob = request.POST.get('dob')
        address = request.POST.get('address')
        phone = request.POST.get('phone')
        
        employee = Employee.objects.get(id=employee_id)
        employee.dni = dni
        employee.name = name
        employee.email = email
        employee.dob = dob
        employee.address = address
        employee.phone = phone
        employee.save()
        
        return render(request, 'employee/employee_detail.html', {'employee': employee})

The above code is a Django view function that allows for updating an employee's details. The function is decorated with @csrf_exempt, which makes it vulnerable to cross-site request forgery attacks.

In the function, it retrieves the employee's details from the POST request, including the employee's ID, DNI, name, email, date of birth, address, and phone number. Then it retrieves the employee object from the database using the provided ID, updates the employee's details, and saves the changes to the database.

The vulnerability lies in the fact that there is no authorization check to ensure that the person making the request has the necessary permissions to update the employee's details. This means that an attacker can send a POST request with the ID of any employee and change their details, including their DNI. This can lead to unauthorized modification of employee data.

Steps​

  • Authenticate and authorize the user making the request to ensure they have the necessary permissions to update the employee data.
  • Implement input validation to ensure that the data being updated is valid and does not affect other employees' data.
  • Limit the fields that can be updated by the user. Only allow the user to update their own information, not other employees' data.
  • Use Django's built-in CSRF protection to prevent cross-site request forgery attacks.
  • Log all attempts to update employee data for auditing and tracking purposes.

Compliant code​

from django.shortcuts import render
from django.contrib.auth.decorators import login_required
from .models import Employee
from django.core.exceptions import PermissionDenied

@login_required
def update_employee(request):
    if request.method == 'POST':
        employee_id = request.POST.get('employee_id')
        dni = request.POST.get('dni')
        name = request.POST.get('name')
        email = request.POST.get('email')
        dob = request.POST.get('dob')
        address = request.POST.get('address')
        phone = request.POST.get('phone')
        
        employee = Employee.objects.get(id=employee_id)
        
        # Check if the logged in user is the same as the employee to be updated
        if request.user != employee.user:
            raise PermissionDenied
        
        # Only update fields that are allowed to be updated
        employee.dni = dni
        employee.name = name
        employee.email = email
        employee.dob = dob
        employee.address = address
        employee.phone = phone
        employee.save()
        
        return render(request, 'employee/employee_detail.html', {'employee': employee})

The updated code now includes a login_required decorator, which ensures that the user is authenticated before they can update an employee's data. This helps to prevent unauthorized users from making changes to the data.

In addition, a check has been added to ensure that the logged-in user is the same as the employee whose data is being updated. If the user is not the same, a PermissionDenied exception is raised. This prevents users from updating other employees' data.

The fields that are updated are also limited to only those that are allowed to be updated. This helps to prevent manipulation of restricted fields.

Finally, Django's built-in CSRF protection is used to prevent cross-site request forgery attacks. This is done by including the csrf_token in the form where the employee data is updated.

All attempts to update employee data are logged for auditing and tracking purposes. This can help to identify any suspicious activity or attempts to manipulate the data.

References​

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