Django url arg cannot contain NUL (0x00) characters

Question

I'm currently testing our site for security vulnerabilities with a very limited background in security myself.

When running the following request:

http://127.0.0.1:8000/stuff/?template=%2Fe%00

I see the error (full stack trace below):

Exception Type: ValueError at /stuff/
Exception Value: A string literal cannot contain NUL (0x00) characters.

This would seem to be a problem with validating url args, and that the character 0x00 (null) shouldn't be allowed. I'm fairly sure that in google's gruyere i saw that some characters should be escaped, but it seems odd to escape null.

I could of course just try/except line 92 in /code/stuff/views.py , but this will no doubt crop up elsewhere.

My questions are thus:

• In django what is the best practice for avoiding XSS attacks via the URL?
• Is this alredy handled (i cant see it in the resolver) somewhere?
• Should this be handled elsewhere completely?

Stack trace:

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  115.                 response = self.process_exception_by_middleware(e, request)

File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  113.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/usr/local/lib/python3.6/site-packages/django/views/generic/base.py" in view
  71.             return self.dispatch(request, *args, **kwargs)

File "/usr/local/lib/python3.6/site-packages/django/views/generic/base.py" in dispatch
  97.         return handler(request, *args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/django/views/generic/list.py" in get
  157.         context = self.get_context_data()

File "/code/stuff/views.py" in get_context_data
  92.         context = super(StuffListView, self).get_context_data(**kwargs)

File "/usr/local/lib/python3.6/site-packages/django/views/generic/list.py" in get_context_data
  119.             paginator, page, queryset, is_paginated = self.paginate_queryset(queryset, page_size)

File "/usr/local/lib/python3.6/site-packages/django/views/generic/list.py" in paginate_queryset
  69.             page = paginator.page(page_number)

File "/usr/local/lib/python3.6/site-packages/django/core/paginator.py" in page
  70.         number = self.validate_number(number)

File "/usr/local/lib/python3.6/site-packages/django/core/paginator.py" in validate_number
  48.         if number > self.num_pages:

File "/usr/local/lib/python3.6/site-packages/django/utils/functional.py" in __get__
  80.         res = instance.__dict__[self.name] = self.func(instance)

File "/usr/local/lib/python3.6/site-packages/django/core/paginator.py" in num_pages
  97.         if self.count == 0 and not self.allow_empty_first_page:

File "/usr/local/lib/python3.6/site-packages/django/utils/functional.py" in __get__
  80.         res = instance.__dict__[self.name] = self.func(instance)

File "/usr/local/lib/python3.6/site-packages/django/core/paginator.py" in count
  91.             return c()

File "/usr/local/lib/python3.6/site-packages/django/db/models/query.py" in count
  392.         return self.query.get_count(using=self.db)

File "/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py" in get_count
  504.         number = obj.get_aggregation(using, ['__count'])['__count']

File "/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py" in get_aggregation
  489.         result = compiler.execute_sql(SINGLE)

File "/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py" in execute_sql
  1100.             cursor.execute(sql, params)

File "/usr/local/lib/python3.6/site-packages/django/db/backends/utils.py" in execute
  99.             return super().execute(sql, params)

File "/usr/local/lib/python3.6/site-packages/django/db/backends/utils.py" in execute
  67.         return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)

File "/usr/local/lib/python3.6/site-packages/django/db/backends/utils.py" in _execute_with_wrappers
  76.         return executor(sql, params, many, context)

File "/usr/local/lib/python3.6/site-packages/django/db/backends/utils.py" in _execute
  84.                 return self.cursor.execute(sql, params)

Exception Type: ValueError at /stuff/
Exception Value: A string literal cannot contain NUL (0x00) characters.

Answer 1

Based on the traceback, the issue isn't that an URL argument couldn't contain %00 , but by the time it's being passed through to the database you're using, through the Paginator , the database driver is complaining about things.

Judging by the error, you're probably using Postgres. (See this related question: Django + Postgres: A string literal cannot contain NUL (0x00) characters )

If you like, you could set up a middleware that rejects any and all request containing %00 .