Cisco warns of another IOS security flaw

Rethink IT, Oct, 2004

Cisco has warned of another security weakness in its products, this time one that could allow an attacker to disable remote administration access to a Cisco device running the network operating system IOS.

The vendor says that a string of specifically crafted TCP packets sent to a port 23 telnet connection, or reverse telnet port, on an IOS-based Cisco router or switch, could block all telnet Remote Shell (RSH), Secure Shell (SSH) and HTTP access to the device Telnet, reverse telnet (a method for telnet access to multiple devices), RSH, SSH and HTTP connections made before an attack would still be intact.

Cisco says that packet forwarding and routing services of the attacked devices would not be affected, but the attack would block net managers' ability to administer or configure the device. This would require them to take the switch or router down to make configuration changes.

Cisco says it will provide an IOS software fix for the vulnerability The vendor says users can work around the problem by disabling telnet and keeping SSH open for remote management.

The vulnerability is the second one reported by Cisco in a week, after it notified users that two of its Access Control Server products could be vulnerable to denial of service attacks or unauthorized log in attempts.