In Juniper Networks Junos OS Evolved receipt of a stream of specific genuine Layer 2 frames may cause the Advanced Forwarding Toolkit (AFT) manager process (Evo-aftmand) responsible for handling Route Class-of-Service (CoS) Firewall operations within the packet forwarding engine (PFE) to crash and restart leading to a Denial of Service (DoS) condition. By continuously sending this specific stream of genuine Layer 2 frames an attacker can repeatedly crash the PFE causing a sustained Denial of Service (DoS). This issue affects Juniper Networks Junos OS Evolved: All versions prior to 20.4R1-EVO. This issue does not affect Junos OS versions.