Cisco IOS XR 3.4.0 through 3.9.1, when BGP is enabled, does not properly handle unrecognized transitive attributes, which allows remote attackers to cause a denial of service (peering reset) via a crafted prefix announcement, as demonstrated in the wild in August 2010 with attribute type code 99, aka Bug ID CSCti62211.
https://exchange.xforce.ibmcloud.com/vulnerabilities/61443
http://www.vupen.com/english/advisories/2010/2227
http://www.securitytracker.com/id?1024371
http://www.cisco.com/en/US/products/products_security_advisory09186a0080b4411f.shtml
http://secunia.com/advisories/41190
http://mailman.nanog.org/pipermail/nanog/2010-August/024837.html