Blind OS command injection with output redirection

Lab Description

Walkthrough

Step 1: Understanding the Feedback Functionality

Navigating to the Submit Feedback page, you will notice four input fields:

1. Name

2. Email

3. Subject

4. Message

The goal is to determine if one of these fields is vulnerable to command injection and whether the output can be redirected to the writable directory /var/www/images/.

Step 2: Intercepting the Feedback Request

Using Burp Suite, intercept the feedback submission request. Below is an example of a normal intercepted request:

The request contains the user input as parameters, making it a good candidate for injection.

Step 3: Crafting the Payload

Modify the Email parameter to include the following payload:

||whoami>/var/www/images/whoami.txt||

This payload runs the command whoami and saves it

Payload Breakdown:

• || is used to append and execute additional commands.

• whoami retrieves the current user running the application.

• >/var/www/images/whoami.txt redirects the output of the command to a file in the writable directory.

Submit the request with the modified payload.

Step 4: Accessing the Output

To retrieve the saved command output:

1. Note that the application serves images from /var/www/images/ via a parameter filename= in the URL.

2. Navigate to any image URL in your browser

3. modify the parameter to filename=whoami.txt

Visiting the URL, the browser displays the output of the whoami command, confirming that the injection was successful. For example: