Lab: Blind OS command injection with output redirection

PRACTITIONER

This lab contains a blind OS command injection vulnerability in the feedback function.

The application executes a shell command containing the user-supplied details. The output from the command is not returned in the response. However, you can use output redirection to capture the output from the command. There is a writable folder at:

/var/www/images/

The application serves the images for the product catalog from this location. You can redirect the output from the injected command to a file in this folder, and then use the image loading URL to retrieve the contents of the file.

To solve the lab, execute the whoami command and retrieve the output.

Access the lab

Solution

Use Burp Suite to intercept and modify the request that submits feedback.
Modify the email parameter, changing it to:
email=||whoami>/var/www/images/output.txt||
Now use Burp Suite to intercept and modify the request that loads an image of a product.
Modify the filename parameter, changing the value to the name of the file you specified for the output of the injected command:
filename=output.txt
Observe that the response contains the output from the injected command.