Software Engineering Institute

Open Shortest Path First (OSPF) is a routing protocol that provides a means for distributing routing information between routers. The Cisco Internetwork Operating System (IOS) implementation of OSPF contains a vulnerability that allows malformed OSPF packets to cause an affected router to reload. Such packets can be sent by an unauthenticated remote attacker and will result in a denial-of-service condition.

By sending a specially crafted OSPF packet to an affected device, a remote, unauthenticated attacker could cause the device to reload. Repeated exploitation of this vulnerability could result in a denial-of-service condition. In order to exploit this vulnerability, an attacker would need to know several parameters. These parameters include the OSPF area number, netmask, hello, and dead timers, which are configured on the affected device.

Apply a patch

Please refer to the "Software Versions and Fixes" section of the Cisco Advisory for more information on upgrading.

Use OSPF authentication

Cisco recommends using OSPF authentication to mitigate against this vulnerability. Quoting from Cisco's Advisory,

OSPF authentication may be used as a workaround. OSPF packets without a valid key will not be processed. MD5 authentication is highly recommended, due to inherent weaknesses in plain text authentication. With plain text authentication, the authentication key will be sent unencrypted over the network, which can allow an attacker on a local network segment to capture the key by sniffing packets.
For more information on OSPF authentication, please see http://www.cisco.com/warp/public/104/25.shtml.

Restrict access

Use Access Control Lists (ACLs) to block or restrict access to affected devices from untrusted networks. For information on implementing ACLs, please see Cisco's white paper "Protecting Your Core: Infrastructure Protection Access Control Lists".