The prep_reprocess_req function in kdc/do_tgs_req.c in the cross-realm referral implementation in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.7 before 1.7.1 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a ticket request.
http://www.vupen.com/english/advisories/2009/3652
http://www.securityfocus.com/bid/37486
http://www.securityfocus.com/archive/1/508622/100/0/threaded
http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2009-003.txt