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Re: Cisco IOS EIGRP Network DoS

  • From: Rubens Kuhl Jr.
  • Date: Thu Dec 19 23:46:07 2002


And including the SSH bug that also has been published
today(http://www.cisco.com/warp/public/707/ssh-packet-suite-vuln.shtml.), it
seems that a lot of networks will have a very "happy" xmas.


----- Original Message -----
From: "James-lists" <hackerwacker@cybermesa.com>
To: <nanog@merit.edu>
Sent: Thursday, December 19, 2002 6:50 PM
Subject: Cisco IOS EIGRP Network DoS


|
|  ----- 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
|
| Attached text moved here:
|
|
| 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 $) ]
|
|
|  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
|
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|  ==============
|  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?
|
|





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