Cisco IOS XR 3.4.0 through 3.8.1 allows remote attackers to cause a denial of service (session reset) via a BGP UPDATE message with an invalid attribute, as demonstrated in the wild on 17 August 2009.
http://www.cisco.com/en/US/products/products_security_advisory09186a0080af150f.shtml
http://securitytracker.com/id?1022739
http://mailman.nanog.org/pipermail/nanog/2009-August/012719.html