Snorlax Snorlax - 6 months ago 173
Python Question

Change URL to another URL using mitmproxy

I am trying to redirect one page to another by using mitmproxy and Python. I can run my inline script together with mitmproxy without issues, but I am stuck when it comes to changing the URL to another URL. Like if I went to google.com it would redirect to stackoverflow.com

def response(context, flow):
print("DEBUG")
if flow.request.url.startswith("http://google.com/"):
print("It does contain it")
flow.request.url = "http://stackoverflow/"


This should in theory work. I see
http://google.com/
in the GUI of mitmproxy (as GET) but the
print("It does contain it")
never gets fired.

When I try to just put
flow.request.url = "http://stackoverflow.com"
right under the
print("DEBUG")
it won't work neither.

What am I doing wrong? I have also tried
if "google.com" in flow.request.url
to check if the URL contains
google.com
but that won't work either.

Thanks

Answer

Setting the url attribute will not help you, as it is merely constructed from underlying data.

Depending on what exactly you want to accomplish, there are two options.

(1) You can send an actual HTTP redirection response to the client. Assuming that the client understands HTTP redirections, it will submit a new request to the URL you give it.

from mitmproxy.models import HTTPResponse
from netlib.http import Headers

def request(context, flow):
    if flow.request.host == 'google.com':
        flow.reply(HTTPResponse('HTTP/1.1', 302, 'Found',
                                Headers(Location='http://stackoverflow.com/',
                                        Content_Length='0'),
                                b''))

(2) You can silently route the same request to a different host. The client will not see this, it will assume that it’s still talking to google.com.

def request(context, flow):
    if flow.request.url == 'http://google.com/accounts/':
        flow.request.host = 'stackoverflow.com'
        flow.request.path = '/users/'

These snippets were adapted from an example found in mitmproxy’s own GitHub repo. There are many more examples there.

For some reason, I can’t seem to make these snippets work for Firefox when used with TLS (https://), but maybe you don’t need that.

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