Advent of CTF – Day 0 Writeup

Advent of CTF – Day 0 Writeup

Advent of CTF is an advent challenge organized by the Novi Hogeschool and created by Arjen Wiersma. This year’s Advent of CTF is a challenge which refers to an old version of the Advent of CTF site.

In order to get the flag we can use an online service called the The WayBack Machine. On this website we can enter the Advent of CTF URL and pick the earliest timestamp available to us.

Opening the Advent of CTF website through the WayBack Machine results in the following page

We can pick the earliest date available, in our case November the 12th 2020. Opening this page gives us the following

If we inspect the page source we find an interesting string of commented HTML

<!-- Ceasar worked on this you know. Tk9WSXtIRVlfMVNfVGgxU19AX0ZsYTk/fQ== -->

Decoding the BASE64 string inside this comment gives us the flag: NOVI{HEY_1S_Th1S_@_Fla9?}!

On to the next challenge: Advent of CTF – Day 1