Document ID: 60557
Last Updated 2002 December 19
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Original Report: http://www.phenoelit.de/stuff/CiscoEIGRP.txt.
Cisco responded with the following, which is also archived at http://www.cisco.com/warp/public/707/eigrp_issue.html:
Cisco can confirm the statement made by FX from Phenoelit in its message "Cisco IOS EIGRP Network DoS" posted on 2002-Dec-19. The EIGRP implementation in all versions of IOS is vulnerable to a denial of service if it receives a flood of neighbor announcements. EIGRP is a Cisco extension of IGP routing protocol used to propagate routing information in internal network environments.
The workaround for this issue is to apply MD5 authentication that will permit the receipt of EIGRP packets only from authorized hosts. You can find an example of how to configure MD5 authentication for EIGRP at the following URL:
If you are using EIGRP in the unicast mode then you can mitigate this issue by placing appropriate ACL which will block all EIGRP packets from illegitimate hosts. In the following example, the EIGRP neighbor has IP address of 10.0.0.2 and the local router has address 10.0.0.1.
Router# config term Router(config)# access-list 111 permit eigrp host 10.0.0.2 host 10.0.0.1 Router(config)# access-list 111 deny eigrp any host 10.0.0.1
The previous example permits all EIGRP packets throughout the router and into the rest of the network. If you want to block these packets as well then use the following commands instead of the previous example:
Router# config term Router(config)# access-list 111 permit eigrp host 10.0.0.2 host 10.0.0.1 Router(config)# access-list 111 deny eigrp any any
An ACL will not be effective if you are using the default multicast mode of EIGRP neighbor discovery. However, multicast packets should not be propagated through the Internet so an attacker must be on the same local network segment as the target router in order to exploit this issue with multicast advertisements.
At the time of writing this notice Cisco PSIRT does not have a current estimate on when the fix will be available.
Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.
|Updated: Dec 19, 2002||Document ID: 60557|