The Protocol Translation (PT) functionality in Cisco IOS 12.3 through 12.4 and 15.0 through 15.3, when one-step port-23 translation or a Telnet-to-PAD ruleset is configured, does not properly validate TCP connection information, which allows remote attackers to cause a denial of service (device reload) via an attempted connection to a PT resource, aka Bug ID CSCtz35999.