# (write-up) CUHK CTF 2025

Hello everyone, I'm notiam_alfred, a secondary school student and a CTF player. I'd like to share my solutions to a couple of challenges.

I am delighted that my team was in top 10 in CUHK CTF 2025. It would be awesome to be able to participate in more CTF competitions in the future, especially the ones hosted by CUHK. My team aims to get a higher rank next year!

## The Betrayal - Copyright Infringement

Today I'm gonna be doing a write-up about the challenge **The Betrayal - Copyright Infringement**.


This is an **osint** challenge. You're required to gather data on websites and do research about it on google (or other browsers).

A <a href="https://sites.google.com/view/iceypenguinmarketing">website</a> is given for this challenge, so let's take a look at it.


There doesn't seem to have any interesting things located at the home page, so let's take a look at the <a href="https://sites.google.com/view/iceypenguinmarketing/about-us?authuser=0">About Us</a> page.


At the bottom of the page, you'll be able to find 3 names - **Sebastian Arepo**, **Sebastien Rotas** and **Montoya Sator**.

If you have done the challenge **The Betrayal - Remote Intrusion**, you might recognize Sebastian Arepo.


If you search his name on the web, you will find this:


A Linkedin account - **Sebastian Arepo - CEO of Icey Penguin Marketing Agency**. This is most likely to be his account as the name perfectly matches the company he's in and his position in the company.

There doesn't seem to contain any useful information that could help us at the home page. But if you scroll down to **Skills**:


You'll see that you're able to **show all 11 skills** of the person (Sebastian Arepo).

After clicking into it:


One endorsement? I wonder who that can be!


So we've discovered another guy called **Nova Laam**, and he had worked for **Icey Penguin Marketing Agency** for a while, then changed to work at another company called **Caesar King Marketing Limited**.

At first, I thought of using the <a href="https://web.archive.org/">Wayback Machine</a>. If you don't know what it is, it's a tool which allows you to look at previous versions of webpages.


Just type in the website you are looking for. I'll use <a href="minecraft.net/en-us">Minecraft's Official Website</a> as an example.

This is how the website looks like now:


This is how the website looks like in 2017 January:


While I thought that this would be the solution, turns out I came to a dead end.


I need to come up with another way.

While other competitors are still struggling with finding the flag, I realised that the solution is really not as complicated as we thought.

There are two ways that you can obtain the flag. For the first solution, you simply go to <a href="https://www.threads.com/">Threads</a>, then search for "**Caesar King Marketing Limited**".


And there you go. You have the flag! (no one checks the Threads account indeed lol)

The second solution is to go to <a href="https://instagram.com/">Instagram</a>, and search for "**Caesar King Marketing Limited**".


Then you'll be able to see the Threads account.


The flag:
**cuhk25ctf{wHy_d0_yoU_u53_My_1ogo_aS_yOur_bRaNd_ima9e_NjI4Zmw}**

Thank you for all the organizers of this event and the authors of the questions who made this competition possible!