The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.9 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a malformed request packet that does not trigger a response packet.
http://www.vupen.com/english/advisories/2011/0330
http://www.securitytracker.com/id?1025037
http://www.securityfocus.com/bid/46272
http://www.securityfocus.com/archive/1/516299/100/0/threaded
http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-002.txt