Security: Verified HTTPS with SSL/TLS¶

Python with SSL enabled¶

First we need to make sure your Python installation has SSL enabled. Easiest way to check is to simply open a Python shell and type import ssl:

>>> import ssl
Traceback (most recent call last):
  ...
ImportError: No module named _ssl

If you got an ImportError, then your Python is not compiled with SSL support and you’ll need to re-install it. Read this StackOverflow thread for details.

Otherwise, if ssl imported cleanly, then we’re ready to setup our certificates: Using Certifi with urllib3.

libraries:
- name: ssl
  version: latest

Using Certifi with urllib3¶

Certifi is a package which ships with Mozilla’s root certificates for easy programmatic access.

1. Install the Python certifi package:

   $ pip install certifi
   

2. Setup your pool to require a certificate and provide the certifi bundle:

   import urllib3
   import certifi
   
   http = urllib3.PoolManager(
       cert_reqs='CERT_REQUIRED', # Force certificate check.
       ca_certs=certifi.where(),  # Path to the Certifi bundle.
   )
   
   # You're ready to make verified HTTPS requests.
   try:
       r = http.request('GET', 'https://example.com/')
   except urllib3.exceptions.SSLError as e:
       # Handle incorrect certificate error.
       ...
   

Make sure to update your certifi package regularly to get the latest root certificates.

Using your system’s root certificates¶

Your system’s root certificates may be more up-to-date than maintaining your own, but the trick is finding where they live. Different operating systems have them in different places.

For example, on most Linux distributions they’re at /etc/ssl/certs/ca-certificates.crt. On Windows and OS X? It’s not so simple.

Once you find your root certificate file:

import urllib3

ca_certs = "/etc/ssl/certs/ca-certificates.crt"  # Or wherever it lives.

http = urllib3.PoolManager(
    cert_reqs='CERT_REQUIRED', # Force certificate check.
    ca_certs=ca_certs,         # Path to your certificate bundle.
)

# You're ready to make verified HTTPS requests.
try:
    r = http.request('GET', 'https://example.com/')
except urllib3.exceptions.SSLError as e:
    # Handle incorrect certificate error.
    ...

OpenSSL / PyOpenSSL¶

By default, we use the standard library’s ssl module. Unfortunately, there are several limitations which are addressed by PyOpenSSL:

• (Python 2.x) SNI support.

• (Python 2.x-3.2) Disabling compression to mitigate CRIME attack.

To use the Python OpenSSL bindings instead, you’ll need to install the required packages:

$ pip install pyopenssl ndg-httpsclient pyasn1

If cryptography fails to install as a dependency, make sure you have libffi available on your system and run pip install cryptography.

Once the packages are installed, you can tell urllib3 to switch the ssl backend to PyOpenSSL with inject_into_urllib3():

import urllib3.contrib.pyopenssl
urllib3.contrib.pyopenssl.inject_into_urllib3()

Now you can continue using urllib3 as you normally would.

For more details, check the pyopenssl module.

Installing urllib3 with SNI support and certificates¶

By default, if you need to use SNI on Python 2.6 or Python 2.7.0-2.7.8, you have to install PyOpenSSL, ndghttpsclient, and pyasn1 separately. Further, to use certifi you have to install it separately. If you know that you want these dependencies when you install urllib3, you can now do:

pip install urllib3[secure]

This will install the SNI dependencies on Python 2.6 and 2.7 (we cannot yet restrict the microversion for 2.7) and certifi on all versions of Python.

InsecureRequestWarning¶

Unverified HTTPS requests will trigger a warning via Python’s warnings module:

urllib3/connectionpool.py:736: InsecureRequestWarning: Unverified HTTPS
request is being made. Adding certificate verification is strongly advised.
See: https://urllib3.readthedocs.org/en/latest/security.html

This would be a great time to enable HTTPS verification: Using Certifi with urllib3.

For info about disabling warnings, see Disabling Warnings.

InsecurePlatformWarning¶

Certain Python platforms (specifically, versions of Python earlier than 2.7.9) have restrictions in their ssl module that limit the configuration that urllib3 can apply. In particular, this can cause HTTPS requests that would succeed on more featureful platforms to fail, and can cause certain security features to be unavailable.

If you encounter this warning, it is strongly recommended you:

• upgrade to a newer Python version

• upgrade ndg-httpsclient with pip install --upgrade ndg-httpsclient

• use pyOpenSSL as described in the OpenSSL / PyOpenSSL section

For info about disabling warnings, see Disabling Warnings.

SNIMissingWarning¶

Certain Python distributions (specifically, versions of Python earlier than 2.7.9) and older OpenSSLs have restrictions that prevent them from using the SNI (Server Name Indication) extension. This can cause unexpected behaviour when making some HTTPS requests, usually causing the server to present the a TLS certificate that is not valid for the website you’re trying to access.

If you encounter this warning, it is strongly recommended that you upgrade to a newer Python version, or that you use pyOpenSSL as described in the OpenSSL / PyOpenSSL section.

For info about disabling warnings, see Disabling Warnings.

Disabling Warnings¶

Making unverified HTTPS requests is strongly discouraged. ˙ ͜ʟ˙

But if you understand the ramifications and still want to do it…

import urllib3
urllib3.disable_warnings()

logging.captureWarnings(True)

PYTHONWARNINGS="ignore:Unverified HTTPS request" ./do-insecure-request.py