Juniper Junos before 11.4R11 12.1 before 12.1R9 12.2 before 12.2R7 12.3R4 before 12.3R4-S3 13.1 before 13.1R4 13.2 before 13.2R2 and 13.3 before 13.3R1 as used in MX Series and T4000 routers allows remote attackers to cause a denial of service (PFE restart) via a crafted IP packet to certain (1) Trio or (2) Cassis-based Packet Forwarding Engine (PFE) modules.