This indicates an attack attempt to exploit a Denial of Service Vulnerability in Digium Asterisk.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system, via a crafted request.
Digium Asterisk Open Source 13.x prior to 13.19.2
Digium Asterisk Open Source 14.x prior to 14.7.6
Digium Asterisk Open Source 15.x prior to 15.2.2
Digium Certified Asterisk 13.18 prior to 13.18-cert3
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor: