Cisco warns on Catalysis DoS danger

Cisco has advised its customers to reconfigure or upgrade its Catalysis switch software after a flaw was discovered which could allow a denial of service (DoS) attack.

The flaw can be activated by sending an incomplete transmission control protocol (TCP) handshake and can bring down the switch. The Catalysis 6000, 5000, 4500 and 4000 series are all affected, as well as earlier switches that use the same code base.

The company said in a statement: "Cisco is aware that some versions of the Cisco CatOS software may be susceptible to a TCP DoS attack under certain circumstances.

"Cisco has published a security advisory with mitigation techniques and free software upgrade information that may help customers protect themselves from potential exploitation.

"To date, Cisco is not aware of any active exploitations of the vulnerability and is working closely with its customers to address this issue."

The flaw can be fixed by either a software patch or by reconfiguring the switch. Only users of Telnet, HTTP or SSH services are vulnerable.

Full technical details can be found here.