An Improper Validation of Array Index vulnerability in the SIP ALG of Juniper Networks Junos OS on SRX 5000 Series allows a network-based, unauthenticated attacker to cause a Denial of Service (DoS). When an attacker sends an SIP packets with a malformed SDP field then the SIP ALG can not process it which will lead to an FPC crash and restart. Continued receipt of these specific packets will lead to a sustained Denial of Service. This issue can only occur when both below mentioned conditions are fulfilled: 1. Call distribution needs to be enabled: [security alg sip enable-call-distribution] 2. The SIP ALG needs to be enabled, either implicitly / by default or by way of configuration. To confirm whether SIP ALG is enabled on SRX, and MX with SPC3 use the following command: user@host> show security alg status | match sip SIP : Enabled This issue affects Juniper Networks Junos OS on SRX 5000 Series: 20.4 versions prior to 20.4R3-S5; 21.1 versions prior to 21.1R3-S4; 21.2 versions prior to 21.2R3-S3; 21.3 versions prior to 21.3R3-S3; 21.4 versions prior to 21.4R3-S2; 22.1 versions prior to 22.1R2-S2, 22.1R3; 22.2 versions prior to 22.2R3; 22.3 versions prior to 22.3R1-S1, 22.3R2. This issue does not affect Juniper Networks Junos OS versions prior to 20.4R1.