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# lab-2

## File Path Traversal, Traversal Sequences Blocked with Absolute Path Bypass

**Difficulty:** Practitioner

### Lab Description

This lab contains a path traversal vulnerability in the display of product images. The application blocks traversal sequences but treats the supplied filename as being relative to a default working directory.

**Objective:** Retrieve the contents of the `/etc/passwd` file.

### Root Cause

The application blocks traversal sequences such as `../`, but still accepts a user-supplied filename and resolves it relative to a working directory. A vulnerable server that accepts absolute paths will open any file the attacker specifies directly — no traversal required.

### Exploitation

1. Access the lab, open any product page, and open the image in a new tab.
2. Capture the request in Burp Suite.
3. Find the URL endpoint: `GET /image?filename=43.jpg`
4. Replace the filename value with an absolute path:

   ```
   /etc/passwd
   ```
5. Send the request — the contents of `/etc/passwd` are returned in the response.

### Lesson Learned

Blocking traversal sequences (`../`) is not sufficient if the server still accepts and resolves absolute file paths from user input. All user-supplied path input must be validated and canonicalised before use — even if it doesn't contain traversal characters.


---

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