Cisco Security Advisory – Recent versions of Cisco IOS Software support RFC4893 (“BGP Support for Four-octet AS Number Space”) and contain two remote denial of service (DoS) vulnerabilities when handling specific Border Gateway Protocol (BGP) updates. These vulnerabilities affect only devices running Cisco IOS Software with support for four-octet AS number space (here after referred to as 4-byte AS number) and BGP routing configured. The first vulnerability could cause an affected device to reload when processing a BGP update that contains autonomous system (AS) path segments made up of more than one thousand autonomous systems. The second vulnerability could cause an affected device to reload when the affected device processes a malformed BGP update that has been crafted to trigger the issue.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/79831/cisco-sa-20090729-bgp.txt
Source: https://packetstormsecurity.com/files/79831/Cisco-Security-Advisory-20090729-bgp.html