An Improper Input Validation vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent attacker to cause a PFE crash and thereby a Denial of Service (DoS). An FPC will crash and reboot after receiving a specific transit IPv6 packet over MPLS. Continued receipt of this packet will create a sustained Denial of Service (DoS) condition. This issue does not affect systems configured for IPv4 only. This issue affects: Juniper Networks Junos OS All versions prior to 12.3R12-S21; 15.1 versions prior to 15.1R7-S10; 17.3 versions prior to 17.3R3-S12; 18.3 versions prior to 18.3R3-S6; 18.4 versions prior to 18.4R2-S9, 18.4R3-S9; 19.1 versions prior to 19.1R2-S3, 19.1R3-S7; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S7, 19.3R3-S4; 19.4 versions prior to 19.4R3-S5; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S2, 20.4R3; 21.…