This indicates an attack attempt against a Denial of Service vulnerability in Cisco firewall products.
The vulnerability is caused by an error when the vulnerable software handles a UTF encoded http request. It allows a remote attacker to bypass the security checks of vulnerable systems via a crafted HTTP request.
Cisco Secure Intrusion Detection System
Cisco Catalyst 6000 Intrusion Detection System Module
Security Bypass: Remote attackers can bypass security checking of vulnerable systems.
Refer to the vendor's web site for suggested workaround.