Urllib and validation of server certificate
I use python 2.6 and request Facebook API (https). I guess my service could be target of Man In The Middle attacks. I discovered this morning reading again urllib module documentation that : Citation:
Warning : When opening HTTPS URLs, it is not attempted to validate the server certificate. Use at your own risk!
Do you have hints / url / examples to complete a full certificate validation ?
Thanks for your help
Answer
You could create a urllib2 opener which can do the validation for you using a custom handler. The following code is an example that works with Python 2.7.3 . It assumes you have downloaded http://curl.haxx.se/ca/cacert.pem to the same folder where the script is saved.
#!/usr/bin/env python
import urllib2
import httplib
import ssl
import socket
import os
CERT_FILE = os.path.join(os.path.dirname(__file__), 'cacert.pem')
class ValidHTTPSConnection(httplib.HTTPConnection):
"This class allows communication via SSL."
default_port = httplib.HTTPS_PORT
def __init__(self, *args, **kwargs):
httplib.HTTPConnection.__init__(self, *args, **kwargs)
def connect(self):
"Connect to a host on a given (SSL) port."
sock = socket.create_connection((self.host, self.port),
self.timeout, self.source_address)
if self._tunnel_host:
self.sock = sock
self._tunnel()
self.sock = ssl.wrap_socket(sock,
ca_certs=CERT_FILE,
cert_reqs=ssl.CERT_REQUIRED)
class ValidHTTPSHandler(urllib2.HTTPSHandler):
def https_open(self, req):
return self.do_open(ValidHTTPSConnection, req)
opener = urllib2.build_opener(ValidHTTPSHandler)
def test_access(url):
print "Acessing", url
page = opener.open(url)
print page.info()
data = page.read()
print "First 100 bytes:", data[0:100]
print "Done accesing", url
print ""
# This should work
test_access("https://www.google.com")
# Accessing a page with a self signed certificate should not work
# At the time of writing, the following page uses a self signed certificate
test_access("https://tidia.ita.br/")
Running this script you should see something a output like this:
Acessing https://www.google.com
Date: Mon, 14 Jan 2013 14:19:03 GMT
Expires: -1
...
First 100 bytes: <!doctype html><html itemscope="itemscope" itemtype="http://schema.org/WebPage"><head><meta itemprop
Done accesing https://www.google.com
Acessing https://tidia.ita.br/
Traceback (most recent call last):
File "https_validation.py", line 54, in <module>
test_access("https://tidia.ita.br/")
File "https_validation.py", line 42, in test_access
page = opener.open(url)
...
File "/usr/local/Cellar/python/2.7.3/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 1177, in do_open
raise URLError(err)
urllib2.URLError: <urlopen error [Errno 1] _ssl.c:504: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed>