Bug in Internet Explorer which can lead to exception in Django CSRF framework

[Anton Morozov]

I have found a bug in Inernet Explorer which can lead to exception in Django in some cases.

This exception can be reproduced in these conditions:

1. Internet Explorer (7+, but i have not test it in IE 10 beta).
2. Django powered site with enabled CSRF protection.
3. IDN domain on HTTPS (i. e. ​https://пример.испытание).
4. JavaScript sends POST request through XMLHTTPRequest (Ajax).

In this case IE sends to server wrong Referer header, in unicode istead of punycode format (​https://пример.испытание istead of ​https://xn--e1afmkfd.xn--80akhbyknj4f like other browsers). At the same time the Host header is right (in punycode).

This leads to the following exception:

Traceback (most recent call last):

  File "/path/to/django/core/handlers/base.py", line 105, in get_response
    response = middleware_method(request, callback, callback_args, callback_kwargs)

  File "/path/to/middleware/csrf.py", line 169, in process_view
    logger.warning('Forbidden (%s): %s' % (reason, request.path),

UnicodeDecodeError: 'ascii' codec can't decode byte 0xd0 in position 45: ordinal not in range(128)

But even without exception the request will not pass the referer test, as HTTP_REFERER and HTTP_HOST variables will be different.

I have prepared the micro django project with which you can reproduce the problem: settings.py and testcase.py in attachment (remember about IDN domain and HTTPS).

To solve the problem we need to check and correct HTTP_REFERER value at the stage of getting enviroment variables, in HTTP handler. In my projects I use custom WSGI handler (fixwsgi.py in attachment). On its basis it is possible to write a patch for django.core.handlers.wsgi.WSGIRequest and django.core.handlers.modpython.ModPythonRequest.

Sorry for my bad english. I wish common sense is understandable.

[Anton Morozov]

Settings file for test case

[Anton Morozov]

Test case micro project

[Anton Morozov]

Custom WSGI handler that solves the problem

[Luke Plant]

I can't test as I don't have an IDN domain, but accepted on the basis of your description.

[Anton Morozov]

Replying to lukeplant:

I can't test as I don't have an IDN domain, but accepted on the basis of your description.

Luke, if you give me your IP I can set it as A record on subdomain of my IDN.

[Tim Graham]

As this seems to be related to a bug in older versions of IE (unknown if it's a problem with newer versions) and there hasn't been any activity in 3 years, I suggest we close this ticket until it's confirmed to still be a problem.