The mobility extension on Cisco Unified IP 9900 phones with firmware 9.4(.1) and earlier allows remote attackers to cause a denial of service (logoff) via crafted packets, aka Bug ID CSCuq12139.
https://exchange.xforce.ibmcloud.com/vulnerabilities/100726
http://www.securityfocus.com/bid/72481
http://tools.cisco.com/security/center/viewAlert.x?alertId=37341
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2015-0600