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Tuesday, May 2, 2017

3 - Command Injection with Burp for NETGEAR router emulated firmware


COMMAND INJECTION WITH BURP FOR NETGAR ROUTER EMULATED FIRMWARE

- Layout for this exercise:



1 - Introduction

- This exercise is based on the Command Injection attack for NetGear devices registered here:


http://firmware.re/vulns/acsa-2015-001.php




- The vulnerability affects a great range of NetGear products, including the router WNAP320:





- One of the affected scripts is called boardDataWW.php, that will be analyzed for the purpose of attacking it through a Command Injection, sending a crafted input taking advantage of the lack of sanitization:




 - The vulnerable section of the script uses an insecure call to PHP function exec(), accepting any type of input for the parameter 'macAddress':





2 - Setting up the lab

- Unzipping and decompressing the firmware of the NetGear router:







- Extracting the .squashfs file:



- A new folder is extracted:




- Inside, we can find the whole root file system of the firmware, ready to be analyzed:








3 - Analyzing the vulnerable PHP script


- First, let's try to locate the vulnerable script boardDataWW.php, using the command locate:







- Opening boardDataWW.php we find the call to the PHP function exec():






- The parameter 'macAddress' is passed without further sanitization about the standard MAC address format:





- Let's see how exec() works:





4 - Intercepting with Burp

- Once the firmware emulated is available (as done in previous exercise):




- Going to the affected script:



- Enabling the proxy at the browser:




- Launching Burp:









- Enabling Burp to intercept Client requests and Server responses:




- Sending a fake MAC address:



- The message is intercepted:



5 - Launching the attack

- Sending the request to the Repeater:






- Now, let's try to craft the MAC address input so that the content of /etc/passwd is leaked to a file located into the root of the web page:

cp   /etc/passwd   /home/www/passwd # from here it is a comment




- Clicking Go and trying to access passwd from the browser:





- The file passwd is open and saved:




- The content of /etc/passwd has been leaked, so the attack is successful:




- Also, because Burp has been enabled to intercept the Server responses, the whole content is displayed:




- It is interesting to notice that this attack has been launched against an "emulated firmware", and not against an actual physical device.