Cisco Security Advisory – Cisco devices running affected versions of Cisco IOS Software are vulnerable to a denial of service (DoS) attack if configured for IP tunnels and Cisco Express Forwarding.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/81603/cisco-sa-20090923-tunnels.txt
Source: https://packetstormsecurity.com/files/81603/Cisco-Security-Advisory-20090923-tunnels.html