The Network Time Protocol (NTP) is used to synchronize a computer's time with a referenced time source.
Robin Park and Dmitri Vinokurov discovered a flaw in the way ntpd handled certain malformed NTP packets. ntpd logged information about all such packets and replied with an NTP packet that was treated as malformed when received by another ntpd. A remote attacker could use this flaw to create an NTP packet reply loop between two ntpd servers via a malformed packet with a spoofed source IP address and port, causing ntpd on those servers to use excessive amounts of CPU time and fill disk space with log messages. (CVE-2009-3563)
A buffer overflow flaw was found in the ntpq diagnostic command. A malicious, remote server could send a specially-crafted reply to an ntpq request that could crash ntpq or, potentially, execute arbitrary code with the privileges of the user running the ntpq command. (CVE-2009-0159)
All ntp users are advised to upgrade to this updated package, which contains backported patches to resolve these issues. After installing the update, the ntpd daemon will restart automatically.