How to handle https traffic using libmproxy? - ssl

Question

I want to implement a proxy server that intercepts both http and https requests. I came across libmproxy (http://mitmproxy.org/doc/scripting/libmproxy.html) that it is SSL-capable. I start with this simplest proxy that just prints the headers of all requests and responses, and forwards them to clients and servers normally.
#!/usr/bin/env python
from libmproxy import controller, proxy
import os
class Master(controller.Master):
def __init__(self, server):
controller.Master.__init__(self, server)
self.stickyhosts = {}
def run(self):
try:
return controller.Master.run(self)
except KeyboardInterrupt:
self.shutdown()
def handle_request(self, msg):
print "handle request.................................................."
print msg.headers
msg.reply()
def handle_response(self, msg):
print "handle response................................................."
print msg.headers
msg.reply()
config = proxy.ProxyConfig(
cacert = os.path.expanduser("~/.mitmproxy/mitmproxy-ca.pem")
)
server = proxy.ProxyServer(config, 1234)
m = Master(server)
m.run()
Then I configure http and ssl proxy in firefox to 127.0.0.1 port 1234. http seems to work fine as I can see all the headers are printed out. However, when the browser sends https requests, the proxy server does not print anything at all, and the browser displays "the connect was interrupted" error.
Further investigation reveals that the https requests go though the proxy server but not controller.Master. I see that proxy.ProxyHandler.establish_ssl() is being called when there is an https request, but the request does not go though controller.Master.handle_request(). Despite that establish_ssl() is called, the browser does not seem to get any response back. I test this with https://www.google.com.
First, how can I make proxy.ProxyHandler works properly with https requests/responses? Second, how can I modify controller.Master so that it can intercept https requests? I'm also open to other tools that I can build a custom http/https proxy server on top of.

Answer 1

You need to install the mitmproxy CA in the browser you are testing with.
Please see details here ("Installing the mitmproxy CA" section):
http://mitmproxy.org/doc/ssl.html
This solved the problem for me.