RE: Are Fragmentation Attacks Still Used for IDS/IPS Evasion?

["Philippe Bogaerts" <xxradar () radarhack com>]

Hi,
I've seen some firewalls that support inspection of fragmented traffic, but
it does not mean they reassemble the traffic. This should be done at the
endpoint (host or server, or proxy).

I agree that it becomes more difficult to 'fool' firewalls or IPS/IDS with
fragmentation, but myself I had a lot of success with fragroute to bypass
IDS/IPS systems that were able to decrypt SSL traffic. Very few (not to say
none ...) were able to handle fragroute. If they already succeeded to
support IP fragmentation, they certainly messed up when using the TCP
segmentation features present in fragroute.




Regards,
Xxradar
http://www.Radarhack.Com


-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com] On
Behalf Of Harry Hoffman
Sent: Wednesday, September 26, 2007 4:36 AM
To: seclt yuri
Cc: pen-test () securityfocus com
Subject: Re: Are Fragmentation Attacks Still Used for IDS/IPS Evasion?

well, there are a few things to think about...

fragmentation as DOS attacks,
fragmentation as cover for stealth attacks,
incorrectly configured firewalls,
compromised systems on the inside that have a greater level of access 
then on the outside. (internal servers that are separated from Desktops 
from a router and not a firewall... not all that uncommon, unfortunately).

Cheers,
Harry

seclt yuri wrote:
> Yes but this effectively means that fragmentation
> attacks are useless if launched across the 'Net and
> when performing a penetration test without local
> access.
>
> Also, even internal host systems are usually
> segregated from servers and server vlans by a
> firewall, so even then, I can't see how fragmentation
> attacks would be effective.  The only scenario that I
> can think of would be within the same subnet or vlan
> where traffic doesn't pass through a firewall.
>
> Please correct me if I am wrong.  Thank you.
>
> --- Harry Hoffman <hhoffman () ip-solutions net> wrote:
>
> > yep, unfortunately not enough people using host
> > based firewalls and alot 
> > of attacks happen inside of where the firewall
> > protects (i.e. local lan)
> >
> > seclt yuri wrote:
> > > Hi,
> > >   I was just reading up on fragmentation attacks
> > using
> > > fragrouter and fragrouter as a mean of IDS/IPS
> > > evasion.  However, since almost all firewalls both
> > > commercial and free (iptables for examples) now
> > have
> > > support for fragment reassembly, are fragmentation
> > > attacks still effective?  Thanks.
> > >
> > >
> > >        
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