On Juniper Networks Junos OS devices, receipt of a malformed IPv6 packet may cause the system to crash and restart (vmcore). This issue can be trigged by a malformed IPv6 packet destined to the Routing Engine or a transit packet that is sampled using sFlow/jFlow or processed by firewall filter with the syslog and/or log action. An attacker can repeatedly send the offending packet resulting in an extended Denial of Service condition. Only IPv6 packets can trigger this issue. IPv4 packets cannot trigger this issue. This issue affects Juniper Networks Junos OS 18.4 versions prior to 18.4R2-S4, 18.4R3-S1; 19.1 versions prior to 19.1R2-S1, 19.1R3; 19.2 versions prior to 19.2R1-S5, 19.2R2; 19.3 versions prior to 19.3R2-S4, 19.3R3; 19.4 versions prior to 19.4R1-S3, 19.4R2. This issue does not affect Juniper Networks Junos OS prior to 18.4R1.