Cisco 9900 fourth-generation IP phones do not properly perform SDP negotiation, which allows remote attackers to cause a denial of service (device reboot) via crafted SDP packets, aka Bug ID CSCuf06698.
http://www.securityfocus.com/bid/62905
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2013-5526