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TUCoPS :: Cisco :: c07-2140.htm

S21sec-034-en: Cisco VTP DoS vulnerability



S21sec-034-en: Cisco VTP DoS vulnerability
S21sec-034-en: Cisco VTP DoS vulnerability



###############################################################
ID: S21SEC-034-en
Title: Cisco VTP Denial Of Service
Date: 26/01/2007
Status: Vendor contacted, bug fixed
Severity: Medium - DoS - remote from the local subnet
Scope: Cisco Catalyst Switch denial of service
Platforms: IOS
Author: Alfredo Andres Omella, David Barroso Berrueta
Location: http://www.s21sec.com/es/avisos/s21sec-034-en.txt 
Release: Public
###############################################################

				S 2 1 S E C

http://www.s21sec.com 

	           	Cisco VTP Denial Of Service


About VTP
---------

VTP (VLAN Trunking Protocol) is a Cisco proprietary protocol used for  
VLAN centralized management.
For instance, when you configure a VLAN in a switch, the VLAN  
information (the VLAN name and its identifier)
will be configured automatically in all the switches that belong to  
the same VTP domain.


Description of vulnerability
----------------------------

VTP uses Subset-Advert messages to advertise the existing VLANs  
within a VTP domain,
sending a malformed crafted packet it is possible to force a switch  
"crash & reload". In order to trigger the vulnerability,
you need to previously set up the trunking (manually or using  
Yersinia DTP attack).


Affected Versions and platforms
-------------------------------

This vulnerability has been tested against Cisco Catalyst 2950T  
switches with IOS 12.1(22)EA3.
Other versions are probably vulnerable.


Solution
--------

According to Cisco PSIRT, it is already fixed. We don't know all the  
details because
Cisco tagged (back in 2005) the issue as an "internal bug", not as a  
security vulnerability.
Upgrade your IOS to the latest release.


Additional information
----------------------

This vulnerability has been found and researched by:

David Barroso Berrueta dbarroso@s21sec.com 
Alfredo Andres Omella aandres@s21sec.com 

It was found on January 2005 and shown in a real demo at BlackHat  
Europe Briefings 2005 (March 2005) (Yersinia, a framework for layer 2  
attacks).
Some months later, FX from Phenoelit found other VTP vulnerabilities:
http://www.securityfocus.com/archive/1/445896/30/0/threaded 
Cisco released then an answer to FX (http://www.cisco.com/warp/public/ 
707/cisco-sr-20060913-vtp.shtml) but as there is no any comment about  
this
specific vulnerability we suppose that it is not related with this one.

This vulnerability has been implemented in the current Yersinia  
version, under the VTP attacks (see the src/vtp.c file) .
Yersinia homepage: http://www.yersinia.net 

You can find this advisory at:
http://www.s21sec.com/en/avisos/s21sec-034-en.txt 

Other S21SEC advisories availabe at http://www.s21sec.com/en/avisos/ 



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