This indicates an attempt to exploit a denial-of-service vulnerability in the Cisco IP Phone firmware.
The vulnerability is a result of the application's failure to properly process a specially crafted INVITE request. As a result, a remote attacker can exploit this to cause a denial-of-service condition.
Cisco IP Phone 7940
Cisco IP Phone 7960
Denial of service
Upgrade to firmware version 8.6(0) (POS8-6-0) :