Heap-based buffer overflow in Cisco Unified IP Phone 7940, 7940G, 7960, and 7960G running SIP firmware might allow remote SIP servers to execute arbitrary code via a crafted challenge/response message.
https://exchange.xforce.ibmcloud.com/vulnerabilities/40498
http://www.vupen.com/english/advisories/2008/0543
http://www.securitytracker.com/id?1019411
http://www.securityfocus.com/bid/27774
http://www.cisco.com/en/US/products/products_security_advisory09186a0080949c7a.shtml