alert udp any 123 -> any 0:1023 (
msg:"ET DOS Likely NTP DDoS In Progress MON_LIST Response to Non-Ephemeral Port IMPL 0x02";
content:"|00 02 2a|"; offset:1; depth:3;
byte_test:1,&,128,0;
byte_test:1,&,64,0;
byte_test:1,&,4,0;
byte_test:1,&,2,0;
byte_test:1,&,1,0;
threshold:type both,track by_src,count 1,seconds 120;
reference:url,www.symantec.com/connect/blogs/hackers-spend-christmas-break-launching-large-scale-ntp-reflection-attacks;
reference:url,en.wikipedia.org/wiki/Ephemeral_port;
classtype:attempted-dos;
sid:2017965; rev:3;
metadata:created_at 2014_01_14, confidence Medium, signature_severity Major, updated_at 2019_07_26;
)