rspec/rules/S5131/python/how-to-fix-it/django.adoc

=== How to fix it in Django

The following code is vulnerable to cross-site scripting because it returns an HTML response that contains user input.

If you do not intend to send HTML code to clients, the vulnerability can be fixed by specifying the type of data returned in the response.
For example, you can use the `JsonResponse` class to return JSON messages securely.

==== Non-compliant code example

[source,python,diff-id=1,diff-type=noncompliant]
----
from django.http import HttpResponse
import json

def index(request):
    json = json.dumps({ "data": request.GET.get("input") })
    return HttpResponse(json)
----

==== Compliant solution

[source,python,diff-id=1,diff-type=compliant]
----
from django.http import JsonResponse

def index(request):
    json = { "data": request.GET.get("input") }
    return JsonResponse(json)
----

It is also possible to set the content-type manually with the `content_type` parameter when creating an `HttpResponse` object.

==== Non-compliant code example

[source,python,diff-id=2,diff-type=noncompliant]
----
from django.http import HttpResponse

def index(request):
    return HttpResponse(request.GET.get("input"))
----

==== Compliant solution

[source,python,diff-id=2,diff-type=compliant]
----
from django.http import HttpResponse

def index(request):
    return HttpResponse(request.GET.get("input"), content_type="text/plain")
----

=== How does this work?

If the HTTP response consists of HTML code, it is highly recommended to use a template engine like https://docs.djangoproject.com/en/4.0/topics/templates/[Django's template system] to generate it.
The Django template engine separates the view from the business logic and automatically encodes the output of variables, drastically reducing the risk of cross-site scripting vulnerabilities.

If you do not intend to send HTML code to clients, the vulnerability can be fixed by telling them what data they are receiving with the `content-type` HTTP header.
This header tells the browser that the response does not contain HTML code and should not be parsed and interpreted as HTML.
Thus, the response is not vulnerable to reflected cross-site scripting.

For example, setting the Content-Type HTTP header to `text/plain` allows to safely reflect user input, because browsers will not try to parse and execute the response.

=== Pitfalls

include::../../common/pitfalls/content-types.adoc[]

include::../../common/pitfalls/validation.adoc[]

=== Going the extra mile

include::../../common/extra-mile/csp.adoc[]