The SRX flowd process, responsible for packet forwarding, may crash and restart when processing specific multicast packets. By continuously sending the specific multicast packets, an attacker can repeatedly crash the flowd process causing a sustained Denial of Service. This issue affects Juniper Networks Junos OS on SRX Series: 12.3X48 versions prior to 12.3X48-D90; 15.1X49 versions prior to 15.1X49-D180; 17.3 versions; 17.4 versions prior to 17.4R2-S5, 17.4R3; 18.1 versions prior to 18.1R3-S6; 18.2 versions prior to 18.2R2-S4, 18.2R3; 18.3 versions prior to 18.3R2-S1, 18.3R3; 18.4 versions prior to 18.4R2; 19.1 versions prior to 19.1R1-S1, 19.1R2.