This indicates an attack attempt to exploit a Denial of Service Vulnerability in Digium Certified Asterisk.
A remote attacker could exploit this vulnerability by sending a crafted MESSAGE request to a vulnerable Asterisk server. Successful exploitation could result in denial-of-service conditions on the Asterisk service.
Digium Asterisk Open Source 13.x prior to 13.27.1
Digium Asterisk Open Source 15.x prior to 15.7.3
Digium Asterisk Open Source 16.x prior to 16.4.1
Digium Certified Asterisk prior to 13.21-cert4
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.