source: http://www.securityfocus.com/bid/25352/info

Cisco IOS is prone to a remote denial-of-service vulnerability because the software fails to properly handle certain CLI commands.

To issue commands that trigger this vulnerability, attackers must be able to successfully authenticate to vulnerable devices. This may be achieved through remote anonymous means or by sending specially crafted input to web interfaces such as 'Looking Glass' web applications.

Successfully exploiting this issue allows attackers to trigger device reboots, denying service to legitimate users.

This issue is documented as Cisco bug ID CSCsb08386.

Cisco IOS releases in the 12.0, 12.1, 12.2, 12.3, and 12.4 ranges are vulnerable to this issue. 

show ip bgp regexp (.*)(_\1)+
show ip bgp regexp ([0-9]*)(_\1)+ 