The kdc_handle_protected_negotiation function in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.8.x, 1.9.x before 1.9.5, and 1.10.x before 1.10.3 attempts to calculate a checksum before verifying that the key type is appropriate for a checksum, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized pointer free, heap memory corruption, and daemon crash) via a crafted AS-REQ request.
http://www.mandriva.com/security/advisories?name=MDVSA-2012:120
http://www.debian.org/security/2012/dsa-2518
http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2012-001.txt
http://rhn.redhat.com/errata/RHSA-2012-1131.html
http://lists.opensuse.org/opensuse-updates/2012-08/msg00016.html