django-debreach

Basic mitigation against the BREACH attack for Django projects.

When combined with rate limiting in your web-server the techniques here should provide at least some protection against the BREACH attack.

Installation

Install from PyPI using:

$ pip install django-debreach

If installing from git you'll also need to install the PyCrypto library.

Add to your INSTALLED_APPS:

INSTALLED_APPS = (
    ...
    'debreach',
    ...
)

Configuration

CSRF token masking

To mask CSRF tokens in the template add the debreach.context_processors.csrf to the end of your TEMPLATE_CONTEXT_PROCESSORS:

TEMPLATE_CONTEXT_PROCESSORS = (
    ...
    'debreach.context_processors.csrf',
)

And add the debreach.middleware.CSRFCryptMiddleware to your middleware, before django.middleware.csrf.CSRFMiddleware:

MIDDLEWARE_CLASSES = (
    'debreach.middleware.CSRFCryptMiddleware',
    ...
    'django.middleware.csrf.CSRFMiddleware',
    ...
)

This works by AES encrypting the CSRF token when it is added to the template, so that {% csrf_token %} now produces a hidden field with a value that is "<random-crypt-text>$<actual-csrf-token-encrypted-with-random-crypt-text>". Then, when the form is POSTed, the middleware decrypts the CSRF token back into it's original form. This ensures that the CSRF content is never the same between requests.

Content length modification

To also randomise the content length of HTML content, add the debreach.middleware.RandomCommentMiddleware to the start of your middleware, but before the GzipMiddleware if you are using that.

This works by adding a random string of between 12 and 25 characters as a comment to the end of the HTML content.