The MITRE CVE dictionary describes this issue as:
The ssl.match_hostname function in the SSL module in Python 2.6 through 3.4 does not properly handle a '\\0' character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.
Find out more about CVE-2013-4238 from the
MITRE CVE dictionary dictionary and
This issue does not affect the version of python as shipped with Red Hat Enterprise Linux 5. The Red Hat Security Response Team has rated this issue as having moderate security impact, a future update may address this flaw.