Cisco released a Security Advisory that a denial-of-service (DoS) condition exists that affects Catalyst 4000, 5000 and 6000 series swicthes running CatOS.
The advisory states that there is a software update available to fix the flaw for all affected customers.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.