Initial Reconnaissance

Even though this is an IDOR-focused room, I started with a quick Nmap scan to check exposed services.

~$ nmap -sV 10.49.151.21

The scan completed cleanly and confirmed that the host was reachable. Only two TCP ports were open.

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.5
80/tcp open  http    Apache httpd 2.4.53

SSH was open, but the web service on port 80 was clearly the main attack surface.

Web Exploitation

I navigated to the web application running on port 80 and was presented with a simple login interface.

At first glance, the page looked intentionally minimal. One detail stood out immediately: a message below the login form referencing a guest account, along with a hint to inspect the page source (Ctrl+U).

Opening the source code revealed a commented line that hadn’t been removed during development:

<!-- use guest:guest credentials until registration is fixed. "admin" user account is off limits!!!!! -->

That single comment explained the next step without needing any guesswork. I logged in using the provided guest credentials.

Once authenticated, I was redirected to a profile page associated with the guest user.

Capturing the Flag

While reviewing the page, I noticed the structure of the URL in the address bar:

http://10.49.151.21/profile.php?user=guest

The application was directly referencing the username as a request parameter. I modified the value of the user parameter in the URL and loaded the page again.

The response changed immediately, and the protected content became visible. The flag was displayed directly on the page.

flag{66be95c478473d91a5358f2440c7af1f}

Conclusion

This room was short and straightforward, but it highlights a real-world issue that often gets overlooked. A simple lack of proper authorization checks was enough to expose another user’s data. Challenges like this reinforce why access control matters just as much as authentication in web applications.

Thanks for taking the time to read this walkthrough.

For more TryHackMe labs and writeups, check out my GitHub repository:
🔗 THM Walkthroughs

More walkthroughs will be added as I continue solving new rooms.