Cisco released an advsiory today that ALL Cisco routers running Cisco IOS that are configured to process IPv4 packets are vulnerable to a denial-of-service condition.

Here is an excerpt from the advisory:

Cisco routers and switches running Cisco IOS® software and configured to process Internet Protocol version 4 (IPv4) packets are vulnerable to a Denial of Service (DoS) attack. A rare sequence of crafted IPv4 packets sent directly to the device may cause the input interface to stop processing traffic once the input queue is full. No authentication is required to process the inbound packet. Processing of IPv4 packets is enabled by default. Devices running only IP version 6 (IPv6) are not affected. A workaround is available.
To read the full advisory and the suggested workaround click here: Cisco Advisory