Cisco 7940/7960 Voice over IP (VoIP) phones do not properly check the Call-ID, branch, and tag values in a NOTIFY message to verify a subscription, which allows remote attackers to spoof messages such as the "Messages waiting" message.
https://exchange.xforce.ibmcloud.com/vulnerabilities/21260
https://euvd.enisa.europa.eu/vulnerability/EUVD-2005-2182
http://www.securitytracker.com/alerts/2005/Jul/1014406.html
http://pentest.tele-consulting.com/advisories/05_07_06_voip-phones.txt