The Intrusion Prevention System (IPS) feature for Cisco IOS 12.4XE to 12.3T allows remote attackers to bypass IPS signatures that use regular expressions via fragmented packets.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5858
https://exchange.xforce.ibmcloud.com/vulnerabilities/32473
http://www.vupen.com/english/advisories/2007/0597
http://www.securitytracker.com/id?1017631
http://www.securityfocus.com/bid/22549
http://www.cisco.com/en/US/products/products_security_response09186a00807e0a5e.html
http://www.cisco.com/en/US/products/products_security_advisory09186a00807e0a5b.shtml