Secunia

Two vulnerabilities have been reported in Cisco IOS, which can be exploited by malicious people to cause a DoS (Denial of Service).

1) An unspecified error exists in the processing of BGP update messages. This can be exploited to reload an affected device via a BGP update message that contains specially crafted AS path information, e.g. constructed from more than 1000 autonomous systems.

2) An unspecified error can be exploited to reload an affected device via a specially crafted BGP update message.

Successful exploitation of these vulnerabilities requires the following conditions:
* The affected Cisco IOS software device is a 4-byte AS number BGP speaker.
* The BGP peering neighbor is a 2-byte AS number BGP speaker.

The vulnerabilities are reported in Cisco IOS and Cisco IOS XE with support for RFC4893 ("BGP Support for Four-octet AS Number Space") when being configured for BGP routing. Please see the vendor's advisory for a complete list of affected versions.

Solution
Update to a fixed version (please see the vendor advisory for details).

Provided and/or discovered by
Reported by the vendor.

Original Advisory
http://www.cisco.com/warp/public/707/cisco-sa-20090729-bgp.shtml

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