An Access of Uninitialized Pointer vulnerability in SIP Application Layer Gateway (ALG) of Juniper Networks Junos OS on SRX Series and MX Series allows an unauthenticated, network-based attacker to cause a Denial of Service (DoS). When specific valid SIP packets are received the PFE will crash and restart. This issue affects Juniper Networks Junos OS on SRX Series and MX Series: 20.4 versions prior to 20.4R3-S4; 21.1 versions prior to 21.1R3-S2; 21.2 versions prior to 21.2R3-S2; 21.3 versions prior to 21.3R2-S2, 21.3R3; 21.4 versions prior to 21.4R1-S2, 21.4R2; 22.1 versions prior to 22.1R1-S1, 22.1R2. This issue does not affect Juniper Networks Junos OS versions prior to 20.4R1.