Inshall'hack
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Inshall'hack

Pizzagate Writeup (34C3 CTF)

Pizzagate was the hardest Web challenge in the 34C3 Junior CTF, which Inshall'hack unfortunately solved 10 minutes after the end of the CTF. Nevertheless, it was quite interesting and therefore deserves a writeup.

Challenge description

pizzagate - hard-ish

We found this [pizza shop]. It seems to be under construction currently, but we believe the whole shop is a
just a front for some fishy business. Is the Italian Mafia behind all this?

Grab your OWASP Top 10 list and investigate! We need to find out what's going on!

Under construction

Upon clicking on the link, I stumble upon the following page:

Under construction

The source of the page contains this comment:

<!-- TODO move actual index back here when development is done -->

… Well let's go for random tests then! Let's try to fetch /index.

Django debug

Luckily this yields results right away in the shape of a Django debug page. Naturally, I try to access /admin right away, but it just redirects to /. Well, that was worth a try… /robots.txt doesn't contain any useful information, and the same goes for /static. /foobarbaz, however, demands that I authenticate as it leads to a devs_only zone.

Dev realm

Bypassing authentication

I immediately try to access the page using an invalid HTTP verb. This allows me to bypass the login page, but it is unfortunately insufficient as I get the following page:

CSRF token missing

Tough luck. Guess I'm going to have to actually authenticate in some way. I try a few common injections, and notice that when using " as the username, the WWW-Authenticate response header is different than usual: it goes from WWW-Authenticate: Basic realm=devs_only err=You provided invalid credentials. to WWW-Authenticate: Basic realm=devs_only err=Unexpected Exception: Invalid predicate. Seems like I broke something.

I quickly assume that the server-side query looks something like username="<username>" AND password="<password>". I therefore craft the following payload in the username field: " or 1=1 or "1"="1. Notice the second condition, that can pretty much return any valid expression; while it can be anything, it is still required as AND has a higher precedence than OR (if AND is × and OR is +, 0 + 1 * 0 = 0, while 0 + 1 + x * 0 = 1).

The injection works, but I am still met with a rather explicit error: WWW-Authenticate: Basic realm=devs_only err=Your username is 'bernd' and your role is 'inactive', but 'admin' role required.. Well, let's just fix the payload, which becomes " or role="admin" or "1"="1. Aaaand, I'm in!

Within the deep site

I'm met with the following page.

Deep pizza

Gotta say it feels quite good to finally access some content! Let's check out all the pages I have access to:

Menu

This menu page also contains the following comment:

<!--<li><b>Pizza itanimullI</b> - Annuit coeptis - Novus ordo seclorum -  1337€</li>-->

Might be a hint of what to buy!

Sign Up

Likewise, the code of this page contains an interesting non-displayed input field:

<input type="hidden" name="role" value="user">

With all that in mind, let's try to sign up with an admin role.

Invalid value 'admin' for user role. Only 'user' and 'dev' supported.

Okay, that's straightforward. Let's create a dev account!

Available pizzas

Now, I can create custom pizzas. Let's try to create one named Pizza itanimullI as described in the comment from the menu page. However, I get the following response:

A pizza with that name exists already!

The account apparently contains 100€ to spend on pizza.

Balance and orders

After a few tries on the order page accessible from this menu, it seems like I am not able to order a Pizza itanimullI. I assume that this is because I do not have the required balance (1337€). In order to fix that, creating a pizza with a negative price springs to mind.

I create a pizza that costs -2000€ and purchase it; I now have a balance of 2100€!

I am now able to purchase a Pizza itanimullI; doing so redirects me to a new, very beautiful part of the site.

Illuminati

The beautiful page

The page basically contains a list of people (illuminati!), among which one can find Donald Trump or Shia LaBeouf, with a link to a video proving they're illuminati. It also contains the following hidden form:

<form role="form" id="form" method="POST">
  <input type='hidden' name='csrfmiddlewaretoken' value='oNpTHcki3KZUnjo7dFXq4sdM13rAvqzCSpv78ObjnhJoVAnpCOtkPnRri68QGrXu' />
  <div class="form-group">
    <label for="illuminatiname">Name the Illuminato</label>
    <input type="text"  name="details" class="form-control">
  </div>            
  <div class="form-group">
    <label for="video">Video ID proof</label>
    <input type="text" class="form-control" id="video" name="video"/>
  </div>
  <button type="submit" class="btn btn-primary">Annult coeptis</button>
</form>

I try it out using the video parameter "lol" and the details parameter "lel". I check out the POST request and notice that it contains another parameter called xml that contains the following code:

<illuminato><details>lel</details><video>lol</video></illuminato>

Once the POST request has gone through, a new entry containing the details/video parameters is added to the list of illuminati. User-passed XML? Smells like an XXE!

After a few tries, I gather that the payload must contain both <video> and <details> tags, and come up with the following XXE:

<?xml version="1.0"?>
        <!DOCTYPE foo [
        <!ENTITY xxe SYSTEM "file:///etc/passwd">
    ]>
    <illuminato>
      <video>whocares</video>
      <details>%26xxe%3B</details>
    </illuminato>

It works, and the content of /etc/passwd is displayed on the page! At this point, it's just about reading the file which contains the line:

flagisinrootinthefileflag:x:1000:1000::/home/flagisinrootinthefileflag:

I modify the request to get /flag instead of /etc/passwd, and voilà!

Flag: 34C3_congratZ_you_know_owasp_and_are_in_the_illumi4nti


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