Cisco routers 9.17 and earlier allow remote attackers to bypass security restrictions via certain IP source routed packets that should normally be denied using the "no ip source-route" command.
Denial of service in Cisco routers running NAT via a PORT command from an FTP client to a Telnet port.
An attacker can identify a CISCO device by sending a SYN packet to port 1999, which is for the Cisco Discovery Protocol (CDP).
Denial of service in Cisco IOS web server allows attackers to reboot the router using a long URL.