Problem

Someone sent me a file with white and black rectangles. I don’t know how to read it. Can you help me?

Attachment: https://ctf.internetwache.org/files/misc70.zip

Solved by 454 teams

Solution

What we get is a packet capture file. I usually approach those with python, but this one was easier to do with just Wireshark.

But first, let’s run strings on it for good measure, two things are interesting:

Authorization: Basic ZmxhZzphenVsY3JlbWE=
...snip...
Content-Disposition: attachment; filename="flag.zip"

The authorization base64 translates to flag:azulcrema.

Now we use Wireshark to extract all HTTP objects, we get two html files and flag.zip. When trying to extract the zip, it asks for a password. What could it be? Hmmm. Let’s try azulcrema… voila! We get a flag.txt.

Flag: IW{HTTP_BASIC_AUTH_IS_EASY}