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Re: Cisco HSRP Weakness/DoS
From: Damir Rajnovic <gaus () cisco com>
Date: Wed, 16 May 2001 07:42:10 +0100

Hello,

Seems that this mail has been lost again.

Gaus

======================
My previous mail seems to be lost due to the mail server problems
so here is the response again.

In response to this mail sent by bashis on Bugtraq:

At 19:57 03/05/2001 +0200, bashis wrote:
I 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.
[truncated, see http://www.securityfocus.com/archive/1/182008]

We 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.

However, there are some other factors that must be considered in
this context:

- 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.

Regards,

Gaus 
==============
Damir Rajnovic <psirt () cisco com>, PSIRT Incident Manager, Cisco Systems
<http://www.cisco.com/warp/public/707/sec_incident_response.shtml>
Phone: +44 7715 546 033
4 The Square, Stockley Park, Uxbridge, MIDDLESEX UB11 1BN, GB
==============
There is no insolvable problems. Question remains: can you 
accept the solution? 


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