chronyd in Chrony before 1.23.1, and possibly 1.24-pre1, generates a syslog message for each unauthorized cmdmon packet, which allows remote attackers to cause a denial of service (disk consumption) via a large number of invalid packets.
https://bugzilla.redhat.com/show_bug.cgi?id=555367
http://www.securityfocus.com/bid/38106
http://www.debian.org/security/2010/dsa-1992
http://secunia.com/advisories/38480