An Incomplete Internal State Distinction vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on SRX 4600 and SRX 5000 Series allows an adjacent attacker to cause a Denial of Service (DoS). If an SRX is configured in L2 transparent mode the receipt of a specific genuine packet can cause a single Packet Processing Engines (PPE) component of the PFE to run into a loop, which in turn will render the PPE unavailable. Each packet will cause one PPE to get into a loop, leading to a gradual performance degradation until all PPEs are unavailable and all traffic processing stops. To recover the affected FPC need to be restarted. This issue affects Juniper Networks Junos OS on SRX 4600 and SRX 5000 Series: 20.1 version 20.1R1 and later versions; 20.2 versions prior to 20.2R3-S7; 20.3 version 20.3R1 and later versions; 20.4 versions prior to 20.4R3-S7; 21.1 versions prior to 21.1R3-S5; 21.2 versions prior to 21.2R3-S3; 21.3 versions prior to 21.3R3-S3; 21.4 versions prior to 21.4R3-S1; 22.1 versions prior to 22.1R3; 22.2 versions prior to 22.2R2; 22.3 versions prior to 22.3R1-S1, 22.3R2.