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 packets 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. For the oldstable distribution , this problem has been fixed in version 1:4.2.2.p4+dfsg-2etch4. For the stable distribution , this problem has been fixed in version 1:4.2.4p4+dfsg-8lenny3. For the testing and unstable distribution, this problem will be fixed soon. We recommend that you upgrade your ntp packages.