Re: Inaccessible Port 80 - Pentest

["Steve Armstrong" <stevearmstrong () logicallysecure com>]

Arvind,

Several people have mentioned firewalls, but stick to layer thee.  I  
believe the barrier you are facing is a layer 7 one.

A mixture of layer 3 port filtering to restrict you to port 80 would  
seem to be inplace.

This could be open to everyone to allow troubleshooting activities.   
However, I believe you are also looking at a layer 7 proxy that is  
restricting access to the service behind it based upon source ip.

The multiple ip addresses could be on the same box thus the strange  
presentation you see.

There are several reasons for wanting this type of restriction. It to  
a certain degree priviatizes the website, is transparent to the end  
user, requires no installation on the client, allows traffic behind  
the FW to be monitored without the need for decryption.  And let's not  
forget permissions can be changed by the admin with no cost or  
implementation lag.

It appears to be hidden in plain sight. Like a VPN without the V and  
some of the P.

As an after thought, were you getting or putting Http data?  Perhaps  
it was a 'collection' server that only allowed clients to post or put  
Http.  That way the clients or agents use common protocols and the  
layer7 FW restricts their http command

HTH

Steve A

---------------------/
Logically Secure

On 8 Aug 2008, at 16:59, "arvind doraiswamy" <arvind.doraiswamy () gmail com 
> wrote:

> Hey Guys,
> Very recently we did a PenTest for a client where we came across a
> strange(atleast to me) situation. Had an IP block which on scanning
> revealed only port 80 open which sounded ok. Any kind of requests
> though from the external world - I tried from multiple IP's and even
> through TOR were blocked by a firewall which kept displaying its
> custom "Access denied" page. So obviously there was some kind of IP
> based restriction in  place which said -- Only these IP's can connect
> to whatever is running on port 80. No problems till here.
>
> My question is: Why would anyone want to  have a live server on the
> Internet, open one port on it and then block it from public use?
> Obvious answers that sprung to mind were:
> a) Maybe its an internal server running a web app to be accessed  
> only internally
>           ----- So why is it public , in the DMZ then? Shouldnt it be
> on the internal network?
> b) Maybe some hosts/apps on the internal network needed to connect to
> port 80 of a DMZ server before going out?
>          ------ Then again why is it public. These servers could be
> placed on an internal segment and the traffic could be NATTEd before
> it goes out like all other Internet destined traffic. And Secondly I
> am not able to think of a situation like this --- What traffic apart
> from a proxy could behave this way --- where I have -- Internal IP
> -------> DMZIP:80 ---------> Internet ? And mind you this wasnt just 1
> IP - there were many, so I'm quite sure I've missed something.
>
> What are your thoughts?
>
> Thnx
> Arvind
>
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