Re: XML firewalls (WAF)

[david () lang hm]

On Thu, 7 May 2009, Chris Hughes wrote:

> After a reply to a previous post I was clued in on XML vulnerabilities with
> web applications.  Off I went to do more reading when I discovered WAF.
> > From what I read, the type of protection afforded by a WAF will address some
> portion of the XML vulnerabilities for both internal as well as externally
> facing web applications.  Now I'm left wondering which web based
> applications actually use XML or other mechanisms (SOAP) that are at risk.
> I have a big MS SharePoint implementation that I'm particularly concerned
> about.
>
>
>
> Is there a way short of calling the vendors to see if they present the risk
> that WAF's allegedly help protect against?

this is similar to asking what applications have vunerabbilities that 
regular firewalls could protect against.

most of the time if the application people knew they would fix the flaws

the problem is that http is being used as a network layer, so just like 
you would not want to allow TCP everywhere without restriction you really 
shouldn't allow http everywhere without restriction.

for some reason many people have trouble understanding this concept, but 
what it really boils down to is that when you implement tunneling, you 
turn the layer that you are using for tunneling into your transport layer, 
and every piece of protection that you would normally put above the 
transport layer needs to be implemented again above the tunneling.

so even if you have a top-notch firewall that does application layer 
checks of the HTTP traffic, as soon as you start tunneling your 
application over it you need to treat it as no better than a packet 
filtering firewall (controlling the source and destination)



different WAF devices do different things, and on top of the device 
capabilities, how good they can possibly be depends on how well you can 
define (or understand) the legitimate traffic that you want to have go 
through it.

if you have documentation of exactly what all your legitimate requests 
look like, you can gain a lot of protection by having the WAF enforce 
these restrictions (in theory this will add zero security because the 
application already did a perfect job of checking it's input. however in 
the real world this can be a significant win)

however, if you can't identify what legitimate traffic looks like, you 
will have serious problems getting much benifit from a WAF. it doesn't 
mean that you can't get any benifit, there are WAFs that try to watch the 
traffic and guess what's 'normal' to configure themselves, but don't fall 
for the trap of assuming that such devices aren't going to require 
understanding the application (and tweaking the configuration) to get much 
use out of them.

David Lang
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