Cisco reports that its Catalyst switches are subject to a potential denial of service.
"After receiving eight TCP connection attempts using a non-standard TCP flags combination, a Catalyst switch will stop responding to further TCP connections to that particular service. In order to re-establish functionality of that service, the switch must be rebooted. There is no workaround. This vulnerability affects only CatOS. No other Cisco products are affected.
More info can be found at http://www.cisco.com/warp/public/707/cisco-sa-20030709-swtcp.shtml