Re: ISA Server and SQL Injection

["Jan P. Monsch" <jan.monsch () csnc ch>]

Hi Arian,

Secondary code injection attacks occur because secondary applications 
often do not do their homework. This is why input validation is often 
proposed as a solution. But it is the most radical solution and most 
intrusive solution.

A developer of a web application does not know what code injection 
problems some exotic or even unknown application in the backend has. Why 
should it be the web application developers problem to solve a code 
injection problem in another application he does not know about. If a 
developer wants to protect any backend application he or she must 
probably block all special characters to be safe against any type of 
code injection attacks. I do not think that this makes sense in the end 
and that the restrictions imposed through this kind of filtering does 
sometimes not meet business requirements. E.g. there are names like 
"D'Amato" which requires a single quote.

Therefore I think that every component should protect itself against 
their own code injection issues. And most achieveable solution is to 
encode any received input properly into output. (Btw. I think that 
SQL-Injection is also a ouput encoding issue - where the output is the 
SQL-Query).

I know from practice that the real world looks different and I therefore 
think that input filter has it value especially if the backend 
applications are not known to be safe against code injection.

Regards Jan



Evans, Arian wrote:
> re: point #2, that's an interesting perspective.
>
> Input validation and cannonicalization has primacy to my mind
> as many attacks are *done* once input is processed, regardless
> of output encoding/error handling.
>
> Additionally, input validation can stop embedded and secondary
> application attacks that the primary application can't control
> (e.g.--application taking input is the data broker for other applications
> that will handle/parse/output the data, from CRM systems to
> administrative applications to log readers).
>
> Ideally those all have proper encoding of their output as well,
> but in reality they often don't.
>
> Using inject script tags (XSS, etc.) as your example, while output
> encoding is an effective defense in certain cases, one problem is
> that you don't always know or control where your output is going.
>
> <OT>
> I see this as more and more of a problem in today's modern, complex,
> distributed computing environments. We plug more and more apps
> together to the point where in some cases pen testing "app X" is as
> silly as pen testing "node 1" on a interconnected network, as appX,
> appY, and appZ are so tied together they really need to be tested
> and treated as one entity, even though they all have a unique UI.
> </OT>
>
> -ae
>
>
> > -----Original Message-----
> > From: Jan P. Monsch [mailto:jan.monsch () csnc ch] 
> > Sent: Tuesday, March 01, 2005 3:37 PM
> > Cc: webappsec () securityfocus com
> > Subject: Re: ISA Server and SQL Injection
> >
> >
> > Hi there!
> >
> > I have lots of discussions with customers regarding the issue of 
> > perimeter application filters. May conclusion regarding the 
> > issue is as 
> > follows:
> >
> > 1. Validation in the application itself is the best and most efficient 
> > way of handling code injection problems. Because the application knows 
> > about its domain but the gateway filter not. In addition the 
> > application 
> > can provide appropriate error messages for incorrect input.
> >
> > 2. Output validation is much better then Input validation, 
> > because most 
> > problems are related to incorrectly encoding input parameters into 
> > output. In addition proper output encoding allows to use critical 
> > characters like < > within the application. This is especially 
> > important 
> > in back-office applications.
> >
> > 3. Output validation should be handled in a security 
> > framework, built by 
> > a security expert. It must be implemented such that the business 
> > developer has not to worry about encoding stuff. (I know this 
> > is a ideal 
> > world szenario)
> >
> > 4. In may opinion validation on the gateway does only make sense if it 
> > used in a transitional way until input/output validation in the 
> > application has been implemented or it is used as a part of intrusion 
> > detection.
> >
> > Regars Jan


--
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Jan P. Monsch
Compass Security Network Computing AG
Glärnischstrasse 7, CH-8640 Rapperswil, Switzerland

Tel +41 55 214 41 67
Fax +41 55 214 41 61
jan.monsch () csnc ch
http://www.csnc.ch

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Security Review - Penetration Testing - Computer Forensics
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