Friday, July 21, 2017

Some Image Based Exploits with their Prevention

Images can be used to run malicious scripts over browser and can also be used to download Trojans if not handled carefully by your website. Too much trust on user input can cause damage to your clients.

In this post, we will run malicious scripts using a simple image viewer functionality and lastly we will discuss on how we can resolve this.

Programming Language
HTML, PHP

Git Repository
https://github.com/csanuragjain/extra/tree/master/ImageExploit

Website
https://cooltrickshome.blogspot.in/2017/07/some-image-based-exploits-with-their.html

One of Image Vulnerability I reported:
https://hackerone.com/reports/221928

Scenario #1:
In this scenario, we will show how lacking Content-Type while displaying images can run malicious scripts.
 Malicious Image




















Description
1)  Right Click on above Image and then Choose Save Image As
2) Name it as exifxss.jpg and Save it.
3) Otherwise you can also get it from the git location.

showImage.php
 <?php  
 include('exifxss.jpg');  
 ?>  


Description
A simple php file which would be showing the above jpg file.

Output:
  1. When you access showImage.php on your browser, you will expect to see the image but instead you will see several pop up coming up.
  2. This happens since the php page is not setting the Content-Type which makes php show image as an HTML. Since Image has several alert messages so they start popping up.
  3. showImage.php need to make sure that it sets the correct Content-Type and also make sure that it does not set the user provided Content-Type.


Scenario #2:
In this scenario, we will show how simple looking image when downloaded can become an exploit.
Caution: This will run notepad, calc, msconfig, services.msc on your computer, although it won't perform anything malicious.

Malicious Image











Description
1)  Right Click on above Image and then Choose Save Image As
2) Name it as exifxss.bat and Save it.
3) Otherwise you can also get it from the git location.

showImage2.html
 <img src="image.bat" width=500 height=500/>  

Description
A simple HTML file showing the image image.bat

Output:

  1. On accessing the above HTML, you would see the bugs bunny image (nothing suspicious)
  2. Now right click on Image and save the image. It would be saved as image.bat
  3. On opening it the malicious payload gets executed opening up notepad, services.msc, msconfig, calc.
  4. To prevent it, make sure that users are never allowed to store any non image extension file.
Please let me know your suggestions and comments.
Hope it helps :)