Robin Park and Dmitri Vinokurov discovered that the daemon component of the ntp package, a reference implementation of the NTP protocol, is not properly reacting to certain incoming packets. An unexpected NTP mode 7 packet with spoofed IP data can lead ntpd to reply with a mode 7 response to the spoofed address. This may result in the service playing packet ping-pong with other ntp servers or even itself which causes CPU usage and excessive disk use due to logging. An attacker can use this to conduct denial of service attacks.