Cisco IOS 12.2(15) and earlier allows remote attackers to cause a denial of service (refused VTY (virtual terminal) connections), via a crafted TCP connection to the Telnet or reverse Telnet port.
Cisco IOS 11.1(x) through 11.3(x) and 12.0(x) through 12.2(x), when configured for BGP routing, allows remote attackers to cause a denial of service (device reload) via malformed BGP (1) OPEN or (2) UPDATE messages.
The Service Assurance Agent (SAA) in Cisco IOS 12.0 through 12.2, aka Response Time Reporter (RTR), allows remote attackers to cause a denial of service (crash) via malformed RTR packets to port 1967.