• Home
  • Blog
  • SSL Certificate Verification failure with fink's Python 2.7.9

SSL Certificate Verification failure with fink's Python 2.7.9

Vincent Danen

January 06, 2015

Python 2.7.9 was released nearly a month ago and with it came some SSL-related changes (it backported the Python 3.4 ssl module and does HTTPS certificate validation using the system's certificate store). The latter can cause some problems with home-grown CA's, however. On Mac OS X, the CA certificate store is in the Keychain Access application which isn't exposed to commandline tools like Python. This will cause HTTPS certificate validation to fail because Python doesn't know anything about the CA certificate used to sign the certificate being used by a HTTPS server.

If you're using the system OpenSSL, supposedly you can export the CA's of interest to the /System/Library/OpenSSL/cert.pem file (untested). I use fink and fink's OpenSSL does not seem to use this directory. Instead it uses /sw/etc/ssl/ and if you install fink's ca-bundle package you will have a stock /sw/etc/ssl/certs/ca-bundle.crt file which presumably works with some applications. This file can be replaced with an updated CA bundle containing the CA certificate that is used to sign the service(s) you want to connect to.

However, replacing that file is not enough. If you upgrade to Python 2.7.9 in fink and make that change, you will still see this annoying error:

[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:581)

when attempting to connect to a site using a certificate signed by a non-stock CA. Note that prior to 2.7.9, Python did not do this CA validation so you would not see this error until upgrading to 2.7.9.

The fix is quite simple. Put your new ca-bundle.crt file in place as noted above, and then, as root, symlink this file to /sw/etc/ssl/cert.pem:

# cd /sw/etc/ssl
# ln -s certs/ca-bundle.crt cert.pem

Now when using Python 2.7.9 (on a fink-using system) you will be able to connect to those sites and avoid the "certificate verify failed" error noted above.

Leave a Comment

Comments use MarkDown. Need help? MarkDown Cheatsheet