Network Time Protocol Package Remote Message Loop Denial of Service Vulnerability

The Network Time Protocol (NTP) package contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
The vulnerability is due to an error in handling certain malformed messages. An unauthenticated, remote attacker could send a malicious NTP packet with a spoofed source IP address to a vulnerable host. Once the host processes the packet, it could send a similar packet to another NTP host. This action could start a message loop between both hosts that could cause them to consume excessive CPU resources and disk space writing messages to log files. These two conditions could cause a DoS condition on the affected hosts.

Functional exploit code is available.

NTP.org has confirmed this vulnerability in a changelog and released updated software.

This vulnerability can be exploited in one of two ways. It can be used to attack a single system running NTP and cause it to send packets to itself. Alternatively, it could be used to target two systems running NTP. In this case, the two systems would rapidly send messages back and forth between each other, causing a DoS condition on each system as well as consuming network bandwidth to carry the messages.