Cisco IOS 12.0 through 12.4, when IP-based tunnels and the Cisco Express Forwarding feature are enabled, allows remote attackers to cause a denial of service (device reload) via malformed packets, aka Bug ID CSCsx70889.
http://www.vupen.com/english/advisories/2009/2759
http://www.securitytracker.com/id?1022930
http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_sep09.html
http://www.cisco.com/en/US/products/products_security_advisory09186a0080af8115.shtml
http://www.cisco.com/en/US/products/products_applied_mitigation_bulletin09186a0080af8113.html
http://tools.cisco.com/security/center/viewAlert.x?alertId=18895