[UTCTF 2022] Baby Shark
15 Mar 2022 by - Dieter
I think someone downloaded something from an http site. Luckily I caught the traffic. I’m super curious about what it was. Let’s go hunt! (doo, doo, doo, doo, doo, doo) By Robert Hill (@Rob H on discord)
Baby shark is a beginner challenge introducing some key web concepts. The challenge provides us with a pcap file and a short description.
For many beginners, the pcap file might be unfamiliar. However with a quick google search, and some context from the description, they can realize that the pcap file stores packet data from a network scan. Or, in other words, stores the traffic over a network. Clearly, we’re going to want to examine this traffic.
To do so, we can utilize a program called Wireshark, as the challenge name alludes to. Opening the file in Wireshark presents us with what seems like gibberish:
The pcap file stores lots of information, much of which is outside the scope of the challenge. A keen eyed viewer might notice that line number 7 contains a GET request for “flag.png”. This is what we’re after. To view the image, simply go to file → export objects → HTTP. This will allow you to export the captured HTTP data. Wireshark will automatically read detect that the file is a PNG, and export it as such.
Opening the PNG, we get our flag!