This indicates an attack attempt to exploit a Denial of Service vulnerability in Digium Asterisk.
The vulnerability is due to an error when the vulnerable application handles crafted SIP Packets. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
Digium Asterisk Open Source 1.8.x prior to 126.96.36.199
Digium Asterisk Open Source 11.x prior to 11.8.1
Digium Asterisk Open Source 12.x prior to 12.1.1
Digium Certified Asterisk 1.8.15 prior to 1.8.15-cert5
Digium Certified Asterisk 11.6 prior to 11.6-cert2
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.