[nsp] Fw: Cisco IOS EIGRP Network DoS

[James-lists]

----- Original Message -----
From: "FX" <fx@phenoelit.de>
To: <bugtraq@securityfocus.com>; <darklab@darklab.org>
Sent: Thursday, December 19, 2002 10:06 AM
Subject: Cisco IOS EIGRP Network DoS


> Hi there,
>
> please find attached an advisory about an issue with the Cisco IOS
Enhanced
> IGRP implementation that can be used to cause a network segment wide
denial of
> service condition.
>
> Regards
> FX
>
> --
>          FX           <fx@phenoelit.de>
>       Phenoelit   (http://www.phenoelit.de)
> 672D 64B2 DE42 FCF7 8A5E E43B C0C1 A242 6D63 B564
>

Cisco comments on Bug traq:

-----BEGIN PGP SIGNED MESSAGE-----

We can confirm the statement made by FX from Phenoelit in his 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
Ciscos' 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 (possibly wrapped):
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/
np1_c/1cprt1/1ceigrp.htm#xtocid18

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 t
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 will permit all EIGRP packet 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 t
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.

The issue with EIGRP neighbor command FX is referring to is assigned
Cisco Bug ID CSCdv19648 and is visible to all registered users through
Cisco's Bug Toolkit at
http://www.cisco.com/cgi-bin/Support/Bugtool/launch_bugtool.pl.
At the time of writing this notice Cisco PSIRT does not have a current
estimate on when the fix will be available.

Gaus

-----BEGIN PGP SIGNATURE-----
Version: PGP 6.5.3

iQEVAwUBPgIFTw/VLJ+budTTAQE7yggAiDxmo8MFD9rULZAG1PKcnn0wfHungE1a
dMfLN1oUaW7LYaMv+PJYkCvSO4t8oJlmQE9MXV3Q9VgLu9FHQDul3tzpOXMCmRB9
19H0XThGXzj7hDUbOrqgYXgDKQucarXg6yZ0nIuxNhEkl4XsnDohaMIkH7ynV/mY
mQ2qIehPw6aus2plvGDKDYZVTbClHk1qjTWhL3AgFqbVH9zkOHppLF47kP/adRlh
GeloUfxwMAJP2w4/MXObHMr9ELY+8mku/Fi0IBMfnZtS/VprZQZuvYQQmov7uYMV
VkvCoI/mkjkJGlTZyxHGtIbQGelC/eub+r4SiCxtH6APiFWaYWnwVw==o5+g
-----END PGP SIGNATURE-----
=============Damir Rajnovic <psirt@cisco.com>, PSIRT Incident Manager, Cisco Systems
<http://www.cisco.com/go/psirt>      Telephone: +44 7715 546 033
200 Longwater Avenue, Green Park, Reading, Berkshire RG2 6GB, GB
=============There is no insolvable problems.
The question is can you accept the solution?

-------------- next part --------------
Phenoelit Advisory <wir-haben-auch-mal-was-gefunden #0815 +++->

[ Title ]
	Cisco Systems IOS EIGRP Network Denial of Service

[ Authors ]
	FX		<fx@phenoelit.de>

	Phenoelit Group	(http://www.phenoelit.de)
	Advisory	http://www.phenoelit.de/stuff/CiscoEIGRP.txt

[ Affected Products ]
	Cisco IOS 

	Tested on:	IOS 11.3
			IOS 12.0(19)
			IOS 12.2

	Cisco Bug ID: 	<not assigned>
        CERT Vu ID:	<not assinged>

[ Vendor communication ]
        10/08/02        Initial Notification,
			gaus@cisco.com
	10/08/02
	   -
	11/14/02	Communication with gaus@cisco.com about the issue,
			fixes and timelines.
	12/18/02 	Final advisory going public as coordinated release
                        *Note-Initial notification by phenoelit
                        includes a cc to cert@cert.org by default

[ Overview ]
	Cisco Systems IOS is vulnerable to a denial-of-service attack using
	Cisco's proprietary routing protocol Enhanced IGRP (EIGRP). When
	flooding a Cisco router with spoofed EIGRP neighbor announcements, 
	the router will cause an Address Resultion Protocol (ARP) storm on 
	the network segment while trying to find the MAC addresses for the
	newly discovered neighbors, effectively using all available bandwidth.
	
[ Description ]
	EIGRP uses automatic discovery of neighboring routers. An EIGRP router
	announces it's existence via multicast on the enabled interfaces. If
	two routers discover each other, they try to exchange information
	about the current topology in unicast. On Ethernet, both sides need 
	to obtain the MAC address of the other router.

	When generating EIGRP neighbor announcements with random source IP
	addresses and flooding a Cisco router (unicast, only possible in 11.x)
	or an entire network (multicast), all receiving Cisco routers will try
	to contact the sender(s). The source IP addresses have to be in the
	subnet(s) enabled via the "network" statement in the config of the
	victim router. 

	A bug in Cisco IOS causes the router to continiously try to obtain the
	MAC address of the sender. This process does not time out unless the
	EIGRP neighbor holdtimer expires. This value is supplied by the sender
	of the neighbor announcement and has a maximum of over 18 hours. 

	Multiple neighbor announcements with not existing source IP addresses
	will cause the router to use all available CPU power and bandwidth on
	the segment for ARP request - creating a segment-wide denial of
	service condition. 
	
	The possible use of IP multicast poses a high risk for larger 
	corporate networks using EIGRP. Cisco IOS versions below 12.0 also
	accept EIGRP neighbor announcements as unicast packets, which makes
	the attack possible via the Internet.
	
[ Example ]
	None provided at this time.

[ Solution ]
	Implement EIGRP authentication using MD5 hashes - which should have
	been done in the first place. Where MD5 can not be implemented, use
	extended access lists to match expected neighbors.

	The obvious workaround of using fixed neighbor entries in the
	configuration does not work due to another bug in IOS that makes it
	ignore the command (Cisco Bug ID CSCdv19648).

[ end of file ($Revision: 1.5 $) ]