A vulnerability was found in NTP. A security issue which enables an off-path attacker to prevent ntpd from synchronizing with NTP servers not using authentication. A server mode packet with spoofed source address sent to the client ntpd causes the next transmission to be rescheduled, even if the packet doesn't have a valid origin timestamp. If the packet is sent to the client frequently enough, it will stop polling the server and not be able to synchronize with it.

NTP is vulnerable to a denial of service, caused by an issue when relying on unauthenticated IPv4 time sources in ntpd. By predicting transmit timestamps for use in spoofed packets, a remote attacker could exploit this vulnerability to cause the daemon to crash or system time change.

An exploitable denial of service vulnerability exists in the origin timestamp check functionality of ntpd 4.2.8p9. A specially crafted unauthenticated network packet can be used to reset the expected origin timestamp for target peers. Legitimate replies from targeted peers will fail the origin timestamp check (TEST2) causing the reply to be dropped and creating a denial of service condition.