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# lab-1

## Remote Code Execution via Web Shell Upload

**Difficulty:** Apprentice

### Lab Description

This lab contains a vulnerable image upload function. It performs no validation on uploaded files before storing them on the server's filesystem.

**Objective:** Upload a basic PHP web shell and use it to exfiltrate the contents of `/home/carlos/secret`. Submit the secret using the button in the lab banner.

**Credentials:** `wiener:peter`

### Root Cause

The developers added no defence against malicious file uploads. With no validation of the filename, extension, or content type, an attacker can upload any file — including a PHP script — and have it stored and served by the server, leading to remote code execution and arbitrary command execution.

### Exploitation

1. Log in as `wiener:peter` and navigate to the account page.
2. Create a file named `php.php` with the following content:

   ```php
   <?php echo file_get_contents('/home/carlos/secret'); ?>
   ```
3. Upload `php.php` as the avatar.
4. Right-click the avatar and select **Open image in new tab** — the server executes the PHP file and the secret is returned in the response.
5. Submit the secret to complete the lab.

### Lesson Learned

Never leave a file upload feature without defences. Accepting files with no validation of filename, extension, or content type allows an attacker to upload and execute arbitrary server-side scripts, leading to remote code execution.


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