An Improper Release of Memory Before Removing Last Reference vulnerability in the Session Initiation Protocol (SIP) Application Layer Gateway (ALG) of Juniper Networks Junos OS allows unauthenticated network-based attacker to cause a partial Denial of Service (DoS). On all MX and SRX platforms, if the SIP ALG is enabled, receipt of a specific SIP packet will create a stale SIP entry. Sustained receipt of such packets will cause the SIP call table to eventually fill up and cause a DoS for all SIP traffic. The SIP call usage can be monitored by "show security alg sip calls". To be affected the SIP ALG needs to be enabled, either implicitly / by default or by way of configuration. Please verify on SRX with: user@host> show security alg status | match sip : Enabled Please verify on MX whether the following is configured: [ services ... rule <rule-name> (term <term-name>) from/match application/application-set <name> ] where either a. name = junos-sip or an application or application-set refers to SIP: b. [ applications application <name> application-protocol sip ] or c. [ applications application-set <name> application junos-sip ] This issue affects Juniper Networks Junos OS on SRX Series and MX Series: 20.4 versions prior to 20.4R3-S2.

21.1 versions prior to 21.1R3-S2.

21.2 versions prior to 21.2R2-S2.

21.2 versions prior to 21.2R3.

21.3 versions prior to 21.3R2.

21.4 versions prior to 21.4R2. This issue does not affect Juniper Networks Junos OS versions prior to 20.4R1. Juniper SIRT is not aware of any malicious exploitation of this vulnerability.