A Stack-based Buffer Overflow vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on MX Series and SRX series allows an unauthenticated networked attacker to cause a flowd crash and thereby a Denial of Service (DoS). Continued receipt of these specific packets will cause a sustained Denial of Service condition. This issue can be triggered by a specific Session Initiation Protocol (SIP) invite packet if the SIP ALG is enabled. Due to this the PIC will be rebooted and all traffic that traverses the PIC will be dropped. This issue affects: Juniper Networks Junos OS 20.4 versions prior to 20.4R3-S2; 21.1 versions prior to 21.1R2-S1 21.1R3; 21.2 versions prior to 21.2R2; 21.3 versions prior to 21.3R2. This issue does not affect Juniper Networks Junos OS versions prior to 20.4R1.