Cisco switches and routers running IOS 12.1 and earlier produce predictable TCP Initial Sequence Numbers (ISNs), which allows remote attackers to spoof or hijack TCP connections.
Cisco IOS 12.0(5)XU through 12.1(2) allows remote attackers to read system administration and topology information via an "snmp-server host" command, which creates a readable "community" community string if one has not been previously created.