TU CTF 2018 - hardDOS

Description

Paying attention is mitey important! (Difficulty: Hard)

nc 18.216.100.42 12345

Solution

This challenge is similar to easyDOS, we have to find the correct commands and arguments.

Also in this case we have to answer some questions before reaching the real challenge.

Let’s just pick one of them.

Of course yes!

Now the real challenge starts. Apparently THE MITE is giving us some hints.

"THE MITE: First thing's first. What's even in here?"

This step was fairly easy, ls is working! We got a list of files and a new hint.

"THE MITE: Alright, seems like a standard DOS installation. One of these files must to have something in it."

We lost quite a lot of time before discovering that the correct command was file. Knowing that we iterate over all files.

"THE MITE: Hey now, GRAPHICS.COM should be a DOS executable!"

So GRAPHICS.COM is the file we are interested in. Eventually one of us tried to do strings GRAPHICS.COM, which gave us the content of the file and the flag!

    TUCTF{4LW4Y5_1NF3C7_7H353_19742_BY735}

Code

flag.py

Cascade

Note that the server was infected by Cascade. Once connected, we only had three minutes before it hits.