The MITRE CVE dictionary describes this issue as:
The pkinit_server_return_padata function in plugins/preauth/pkinit/pkinit_srv.c in the PKINIT implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.10.4 attempts to find an agility KDF identifier in inappropriate circumstances, which allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted Draft 9 request.
Find out more about CVE-2012-1016 from the
MITRE CVE dictionary dictionary and
This issue did not affect the versions of krb5 as shipped with Red Hat Enterprise Linux 5 as they did not include support for PKINIT.