Need

Enforcement of security controls for data creation

Context

Description

from django.db import models

class Policy(models.Model):
    name = models.CharField(max_length=100)
    beneficiaries = models.ManyToManyField('Beneficiary', related_name='policies')

class Beneficiary(models.Model):
    name = models.CharField(max_length=100)

The above code represents a Django model called `Policy` and another model called `Beneficiary`. A policy can have multiple beneficiaries, and this relationship is represented by a Many-to-Many relationship between `Policy` and `Beneficiary`. The `PolicyView` class is a Django view that handles the creation of policies and beneficiaries. In the `post` method, it first gets the policy name and beneficiary names from the POST request. It then creates a policy with the given name and for each beneficiary name, it creates a beneficiary and adds it to the policy. The vulnerability here is that there is no restriction on the number of beneficiaries that can be added to a policy. Despite the business rule that a policy should only have four beneficiaries, the current implementation allows the creation of a policy with any number of beneficiaries. This can lead to potential data integrity issues and can also be exploited by an attacker to create policies with a large number of beneficiaries, leading to potential denial of service.

from django.db import models
from django.core.exceptions import ValidationError

class Policy(models.Model):
    name = models.CharField(max_length=100)
    beneficiaries = models.ManyToManyField('Beneficiary', related_name='policies')

        if self.beneficiaries.count() > 4:...

The code above fixes the vulnerability by adding a custom save method to the `Policy` model. This method checks the count of `beneficiaries` before saving the `Policy` instance. If the count of `beneficiaries` is more than four, it raises a `ValidationError` with a message indicating that a policy cannot have more than four beneficiaries. This ensures that the restriction on the number of beneficiaries is enforced at the model level, preventing the creation of a policy with more than four beneficiaries. This maintains the integrity of the data and prevents the bypassing of this security control.

References