CATAPULT SPIDER - Much Sad

This is an OSINT challenge: find the flag in the publically-available information CATAPULT SPIDER has left online.

Challenge description

We have received some information that CATAPULT SPIDER has encrypted a client's cat pictures and successfully extorted them for a ransom of 1337 Dogecoin. The client has provided the ransom note, is there any way for you to gather more information about the adversary's online presence?

NOTE: Flags will be easily identifiable by following the format CS{some_secret_flag_text}. They must be submitted in full, including the CS{ and } parts.

Solution

We're given a file to download muchsad.txt:

Two things jump out: a Dogecoin wallet address: DKaHBkfEJKef6r3L1SmouZZcxgkDPPgAoE and an email address shibegoodboi@protonmail.com. Plugging shibegoodboi into Google yields a few promising hits: a Twitter account https://twitter.com/shibegoodboi and a Reddit profile https://www.reddit.com/user/shibegoodboi/.

Visiting the Twitter page a link to a GitHub repository https://github.com/shibefan:

In shibefan's repositories is one for https://shibefan.github.io. We can either browse through the repository and view the index.html of the page, or just visit https://shibefan.github.io:

And there's the flag: CS{shibe_good_boi_doge_to_the_moon}

Answer

CS{shibe_good_boi_doge_to_the_moon}