A flaw was found in the Network Time Protocol (NTP), where a security issue exists that allows an off-path attacker to prevent the Network Time Protocol daemon (ntpd) from synchronizing with NTP servers not using authentication. A server mode packet with a spoofed source address sent to the client ntpd causes the next transmission to be rescheduled, even if the packet does not have a valid origin timestamp. If the packet is sent to the client frequently enough, it stops polling the server and is unable to synchronize with it.