[WEB SECURITY] Re: Can HTTP Request Smuggling be blocked by Web Application Firewalls?

Amit Klein (AKsecurity) aksecurity at hotpop.com
Wed Jun 22 03:53:49 EDT 2005

Hi Andrew,

On 22 Jun 2005 at 16:17, Andrew van der Stock wrote:

> Amit,
> I feel that the WAF in this case would increase the likelihood of a  
> HTTP smuggling attack as it participates in the flow, and more than  
> likely interprets HTTP requests differently than pretty much  
> everything else out there. 

Yes, that is possible (as I hinted in my message), if the WAF is between the devices, or if 
the WAF itself is the object of the attack.

If they RST'd dodgy connections and left  
> alone all others, then maybe these devices serve a purpose, but if  
> it's a re-writing proxy, it has to affect the flow.

I agree.

> <rant = on>
> I have been struggling with the point of "security" HTTP proxies  
> recently in several of the projects I've been involved with. The  
> projects were infected by sales people who say "Buy this widget, and  
> all your security problems are over". Nothing could be further from  
> the truth. I recently lost a battle to remove a virus scanning web  
> proxy on a private leased line which transmitted XML provided by MQ  
> Series. The impetus to buy useless things to solve non-existent  
> problems is troubling.
> In my view, unless a proxy understands the underlying data and pages,  
> or XML DTDs if it is looking at SOAP requests, I feel the additional  
> burden of the proxies is rarely worthwhile and just adds one more  
> component which may be abused.
> </rant>

Oh, I wouldn't throw the baby out with the bath water. I think that WAFs (at least in 
theory) are basically good things. I haven't seen a perfect one yet - they all have their 
problems. But I wouldn't dismiss them as useless. 
Don't get me wrong - there are certainly cases where buying and deploying WAF is absurd, 
and there are probably many cases where WAFs are sold as a solution to world hunger, but 
that shouldn't blur our technical view - of what WAFs can and can't do.

I fully agree to the second part of your rant. If a WAF can't understand HTTP, and the 
application logic, and SOAP/XML (if it's supposed to handle XML and web services), then 
obviously it's missing a core security functionality. Merely deploying a simple (mindless) 
HTTP proxy is not going to help in most situations (I believe that's what you're saying).

> Security vendors should perform strict conformance testing and make  
> those results available to potential customers. Something like the  
> old IPsec and cache bake offs or industry certification that these  
> devices are truly RFC compliant would be nice.

Hear! Hear! ;-)

I'll have you know that WASC (Web Application Security Consortium) works on a project 
called  "Web Application Firewall Evaluation Criteria"  
(http://www.webappsec.org/projects/waf_evaluation/) that aims at defining criteria for 
evaluating and comapring WAFs.
When it's complete, hopefully it would be able to address people's needs and reduce the 
hype levels in the market.


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