Writeup: Advent of CTF 0

For the month of December, I’ll be taking part in the Advent of CTF challenges created by @credmp and @NOVIhogeschool. The challenges are available here https://adventofctf.com and are released one per day. Let’s see how far I can go :).

The first challenge took me a minute to figure out. It simply stated:

Do you remember the flag in the teaser website?

Well, I remember there was an announcement page that had been up for a while but I did not search for any flags on that page. We would have to find the previous website in the archives. We can use the WayBackMachine to go back in time. Let’s look for adventofctf.com. We see that it was saved 3 times between November 12, 2020 and November 29, 2020.

When we click on the 12th, we are taken to the archived page that existed on that day.

Using developer tools, let’s inspect the page for anything interesting. Notice the string Tk9WSXtIRVlfMVNfVGgxU19AX0ZsYTk/fQ== that looks like base64 encoding.

Let’s try and decode the string using CyberChef.

The decoded text gives us the flag: NOVI{HEY_1S_Th1S_@_Fla9?} which when submitted, earns us over very first point :). Let’s update the Badge Server too with the same flag.

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