When ntpd as an NTP client receives a Kiss-of-Death (KoD) packet from the server to reduce its polling rate, it doesn't check if the originate timestamp in the reply matches the transmit timestamp from its request. An off-path attacker can send a crafted KoD packet to the client, which will increase the client's polling interval to a large value and effectively disable synchronization with the server. This issue affects ntp versions 4.2.6 and 4.2.8 up to 4.2.8p3. The attacker can find out to what server the client is currently synchronized by sending it a regular client mode packet and checking the refid field in the reply (the refid is IPv4 address or first four bytes of MD5 sum of IPv6 address). Upstream bug: http://bugs.ntp.org/show_bug.cgi?id=2901 http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-7704
