RE: [fw-wiz] CERT vulnerability note VU# 539363

dufresneat_private

Of course the attacks mentioned in this CERT advisory are not really
traffic limit overloads, but, resource exhaustion techniques.  The tcp/syn
flood method of exhhaustion should be well handled by most firewalls these
days.  But, the newer CRC related method is something  even more
interesting.  And seems to support the claims of Marcus and Mikeal and
Paul and others about the real depth and breath of the packet logic in
filtering and stateful as well as proxied gateways.  From how I read the
CERT, it seems you can have speed and performance, or you can have a full
examination of the packets and all their settings, but, perhaps not both
at the sametime, so vendors shoot for the former.

Thanks,

Ron DuFresne

On Wed, 16 Oct 2002, Stephen Gill wrote:

> In my opinion if a stateful firewall claims it can filter at rate X
> (64byte packets, etc...), it should be able to filter at that rate under
> all conditions.  Clearly a 100MB firewall that can be overloaded with
> 1MB of traffic is not good.  I'd argue that if a 100MB firewall can be
> overloaded with 34MB of traffic, it's also not a good thing.  But then
> again, even 100MB of filtering won't save you in a 100MB DoS which is
> not all that uncommon.  
> 
> I'd like to learn some of the other methods being used for mitigation
> amongst vendors.  
> 
> -- steve
> 
> -----Original Message-----
> From: Mikael Olsson [mailto:mikael.olssonat_private] 
> Sent: Wednesday, October 16, 2002 7:44 AM
> To: Stephen Gill
> Cc: firewall-wizardsat_private
> Subject: Re: [fw-wiz] CERT vulnerability note VU# 539363
> 
> 
> Stephen Gill wrote:
> > 
> > Thought I'd pass this along.
> > 
> > http://www.kb.cert.org/vuls/id/539363
> 
> Although this is something that people need to keep in mind when 
> picking / designing a firewall, I'd argue that anything north of
> a stateless packet filter is going to be vulnerable to these sort
> of attacks.  
> 
> If you keep state, you will be vulnerable to state table overflows. 
> Period.  The only real question is: how much work does the attacker 
> need to put in before it becomes painful for the networks that the 
> firewall is protecting?  Is being able to resist a  1 Mbps stream 
> (~4500 pps) "Not vulnerable"?  Is being able resist a 34 Mbps stream
> (~150 kpps) "Not vulnerable"?  Or should every single firewall
> vendor report in and say "Vulnerable", and describe what the limit is?
> 
> 
> And, yes, ALG-only firewalls can also be overloaded. It's just a 
> different type of 'state'.
> 
> 

-- 
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