MD5 Neighbor Authentication in Extended Interior Gateway Routing Protocol (EIGRP) 1.2, as implemented in Cisco IOS 11.3 and later, does not include the Message Authentication Code (MAC) in the checksum, which allows remote attackers to sniff message hashes and (1) replay EIGRP HELLO messages or (2) cause a denial of service by sending a large number of spoofed EIGRP neighbor announcements, which results in an ARP storm on the local network.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5741
http://www.vupen.com/english/advisories/2005/3008
http://www.securityfocus.com/bid/15970
http://www.securityfocus.com/archive/1/419898/100/0/threaded
http://www.securityfocus.com/archive/1/419830/100/0/threaded
http://securitytracker.com/id?1015382
http://securityreason.com/securityalert/274
http://marc.info/?l=full-disclosure&m=113504451523186&w=2
http://lists.grok.org.uk/pipermail/full-disclosure/2005-December/040332.html