Bypass firewall using images

Posted on 2014-01-06
Last Modified: 2014-01-26
I'm new to network administration. I have seen some file comming from internet to our trusted company network as images. When I view these files it displays lots of dots and rendered as a valid image file also.

How can I detect and stop with out stoping the entire web site which hosts the particular images ?

I think we use Checkpoint firewall.

Question by:rpgeegange
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LVL 23

Expert Comment

by:Patrick Bogers
ID: 39761338

Could you be a little more precise about what is happening?
Are there images being uploaded through a web application or ....?
Where are the images been stored and in what format?

Author Comment

ID: 39761361
Hi Patricksr1972,
Thanks for the reply.
These image are stored in free image hosting sites. Downloaded by some program from inside the network.
These images are in png format. I'm not sure it is using stenography.
LVL 23

Expert Comment

by:Patrick Bogers
ID: 39761379
ok, and where are they stored? A share or someone home directory?

What are you thinking? It is some sort of malware?
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Author Comment

ID: 39761406
I'm not sure whether it is a malware or not. because I can see an some doted image in it. They were stored in "my documents".
It can be liked this, malware convert its components to an image then get them through the firewall and then, decode it again.

If it is an malware, how can I stop it ?
LVL 23

Expert Comment

by:Patrick Bogers
ID: 39761412

You could download malwarebytes and have a full scan running, you will know soon enough.

Author Comment

ID: 39761429
how can block images like this ? is there such ways ? I have read about this regarding image blocking mechanisms. how this technology works ? will it helps me ?

LVL 46

Expert Comment

by:Craig Beck
ID: 39772677
You need a UTM device or firewall which can do AV scanning.
LVL 63

Expert Comment

ID: 39772765
Besides the below to chec on the machine downloaded with potential malicious content

Indeed some traditional FW does ICAP means to send files such as images to anti virus server and supposed to offload their performance and this capabilities off box. However there can be limit to file size,  delay and false positive of sending corrupted files choking the entry check. Traditional  FW cannot keep up hence next gen FW and UTM based FW gain traction and bigger appeal. ..there is application delivery content that does this. In all you are  looking deep content inspection with anti malware or bot check coupled with real time threat feeds cum content filtering to prevent badsites reach from user, where possible.

Checkpoint software blades technology is their move into UTM. They are keen competitor to Palo alto which seems to have started the NGFW "trend". Anti APT is all saying to be preventive for the hard sale...nonetheless, you can check this blade and other associated in Checkpoint portfolio

It also couple with content filter or proxy like Websense gateway..but as a whole endpoint serves the next layer if the image bypass and evade. Password protected or obfuscated files easily avoid detection hence breach detection device came to picture like FireEye, XPS, Netwitness, Solera etc...layer checks and no one size fits simple takeaway
LVL 70

Expert Comment

ID: 39772776
Hi, this kind of reminds me of  3D Stereograms
Stereograms are 3D images hidden within another picture.

Is this what you are typically seeing?
Can you determin who is downloading them?
In Sep 15, 2004  Microsoft's monthly security update was highlighted by a JPEG-handling vulnerability that could allow pictures in the format to provide access to remote code execution.
But that was patched way back then.
Do you have Microsoft's Malicious Software Removal Tool  updated from windows updates?
LVL 63

Expert Comment

ID: 39773012
No one good full proof solution as eventually we are going against beyond signature based detection.  You can catch this

What can be done? I believe a key perspective to dealing with this evasion technique is to better understand the suspicious nature of the file transfer. Consider it “contextual awareness”. Despite not being able to dissect and analyze the malicious binary directly, understanding the context of its transport will likely provide enough circumstantial evidence to arrive at a comfortable conclusion as to the maliciousness of the binary
LVL 40

Accepted Solution

noci earned 500 total points
ID: 39774745
This is hard to do, as "images" mean something to us humans. And the representation of that in data is massive. Where small changes in images is hard to notice but can mean much info being "hidden".

You mentioned stenography, but that is a sign language also named shorthand, to note down realtime discussions on paper (like in courthouses etc.).
You probably meant Stegano-graphy or the hiding of info.
You can only prove steganography if you have a picture with and without the message.
Steganography uses  f.e. a text message converted to morse. and then
use the lowest bit in the blue every 16'th pixel to denote a dash or dot.  
You won't detect that ever without comparing to the original image.

And you mention PNG, (which can actually be represented in ascii readable form like a C declaration is needed) what about all the other formats GIF, BMP, JPG, ... etc. etc.

You may need a proxy to have all your transfers checked for pictures containing executable images, whose presence is easier to prove, f.e. if part of the image contains PE and the info after it looks like it could be a program header you can assume it is a windows NT program, or MZ and some valid data it may be a DOS executable etc.

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