WinjaCTF2021: JUSTWINTHIS (300)

This is from the WinjaCTF2021.

For this challenge, we are given he following hint:

Going to the link provided, we get this simple page:

After a bit of poking, I register an account:

When I log in with my new credentials, I am given this message:

Remembering a cipher I once saw that uses emojis, I try and decipher it using

I see it decodes to “ar3_t0kens_$$$}”, which looks a lot like the tail end of a flag!

After some more poking, I see there is a cookie set by this site.

I decode the cookie value (base64) and see it is a JASON Web Token. Knowing how they are formatted, I break up the encoded cookie value and just decode the header to get this:


Seeing the “role” element with a value of “user”, I try changing the value to “admin” and then re-encoding the header and adding the preserved tail end of the original cookie value:


I paste that cookie value into my browser and refresh the page to get this new message:

I just got the first half of the flag.

Combining the two I get the full flag value:


Leave a Reply

Your email address will not be published. Required fields are marked *