Cisco IP Phone 7940 and 7960 with P0S3-08-6-00 firmware, and other SIP firmware before 8.7(0), allows remote attackers to cause a denial of service (device reboot) via (1) a certain sequence of 10 invalid SIP INVITE and OPTIONS messages; or (2) a certain invalid SIP INVITE message that contains a remote tag, followed by a certain set of two related SIP OPTIONS messages.
https://exchange.xforce.ibmcloud.com/vulnerabilities/36125
http://www.vupen.com/english/advisories/2007/2928
http://www.cisco.com/warp/public/707/cisco-sr-20070821-sip.shtml
http://securitytracker.com/id?1018591
http://securityreason.com/securityalert/3042
http://secunia.com/advisories/26547
http://lists.grok.org.uk/pipermail/full-disclosure/2007-August/065402.html
http://lists.grok.org.uk/pipermail/full-disclosure/2007-August/065401.html