(RHSA-2009:1648) Moderate: ntp security update

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)

All ntp users are advised to upgrade to this updated package, which
contains a backported patch to resolve this issue. After installing the
update, the ntpd daemon will restart automatically.