The VPN authentication functionality in Cisco Adaptive Security Appliance (ASA) Software allows remote attackers to cause a denial of service (device reload) by sending many username-from-cert IKE requests, aka Bug ID CSCua91108.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-5384
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2013-5544