Cisco IOS 12.2 through 12.4, when certain PMTUD, SNAT, or window-size configurations are used, allows remote attackers to cause a denial of service (infinite loop, and device reload or hang) via a TCP segment with crafted options, aka Bug ID CSCsz75186.
https://exchange.xforce.ibmcloud.com/vulnerabilities/57129
http://www.vupen.com/english/advisories/2010/0703
http://www.securitytracker.com/id?1023743
http://www.securityfocus.com/bid/38930
http://www.cisco.com/en/US/products/products_security_advisory09186a0080b20f34.shtml