PicoCTF 2017 – Yarn #appsec #infosec #ctf

Another day, another challenge…

Today’s blog post we will solve the, “Yarn” challenge from PicoCTF.

Let’s get started.

Clicking on the challenge we see:

PicoCTF_Yarn_1

OK, we need to find a flag inside of a file, but we do not know what the file is.

Let’s look at the hints and see if that provides any clues.

PicoCTF_Yarn_2

Looking at the hints we’re provided with two questions. Possibly answering these questions will leads us to the flag.

Answer question #1 – “what does the string command use to determine if something is a string?” We decide to do a Google search to answer just that.

Doing this Google search we’re provided with the following link.

Reading the article we determine that the strings command prints the printable characters from a file.

Doing that we’re provided with the following screenshot:

PicoCTF_Yarn_3

We’ve answered question #1. Let’s answer question #2.

Question #2 – is there a way to change the length that the strings command look for?

Going back to the link we see that there is a way we can specify that there is a way to determine the length of strings we want to print.

How do we use this?

By adding the “-n <length you want to use>”

Doing this we get the following:

PicoCTF_Yarn_4

Scrolling down we see:

PicoCTF_Yarn_5

Hmm… I think we found the flag! “Submit_me_for_I_am_the_flag”

Putting this string as the flag we have acquired 55 points!

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