Baby Auth

Analysis

We are first greeted by a login page. Let's, once again, try admin with password admin:

Invalid username or password

Looks like we'll have to create an account - let's try those credentials.

this user already exists

This is great, because now we know we need a user called admin. Let's create another user - I'll use username and password yes, because I doubt that'll be used.

Login Redirect

We're redirected to the login, which makes it seem like it worked. Let's log in with the credentials we just created:

Whoops, guess we're not an admin!

When it comes to accounts, one very common thing to check is cookies. Cookies allow, among other things, for users to authenticate without logging in every time. To check cookies, we can right-click and hit Inspect Element and then move to the Console tab and type document.cookie.

Well, we have a cookie called PHPSESSID and the value eyJ1c2VybmFtZSI6InllcyJ9. Cookies are often base64 encoded, so we'll use a tool called CyberChef to decode it.

Once we decode the base64, we see that the contents are simply {"username":"yes"}.

Exploitation

So, the website knows our identity due to our cookie - but what's to stop us from forging a cookie? Since we control the cookies we send, we can just edit them. Let's create a fake cookie!

Creating a Fake Cookie Value

Note that we're URL encoding it as it ends in the special character =, which usually has to be URL encoded in cookies. Let's change our cookie to eyJ1c2VybmFtZSI6ImFkbWluIn0%3D!

Ignore the warning, but we've now set document.cookie. Refresh the page to let it send the cookies again.

And there you go - we successfully authenticated as an admin!

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