UGGC

Author: roerohan

In this challenge, the goal is to modify the cookies so that you become the admin.

Requirements

• Browser Devtools

Source

• http://jh2i.com:50018/login

Become the admin!

Connect here:
http://jh2i.com:50018

Exploitation

When you type in a random username, for example, csictf, and check the Cookies in the Application tab of Browser Dev-Tools (alternatively console.log(document.cookie)), you see a cookie named user set to pfvpgs. The target is to make the username corresponding to this cookie be admin. This is similar to another Caesar's cipher challenge.

As you see, there is an offset of 13 between the characters in csictf and pfvpgs. Therefore, you can find out the string corresponding to admin by encrypting it with an offset of 13.

>>> print(''.join([chr((ord(i) + 13)) for i in 'admin']))
'nqzv{'

Now, the last character is {, so we subtract 26 to get the required character.

Note: The offset is 13 and we know 'n' maps to 'a', so obviously 'a' will map to 'n', but we'll try it anyway.

>>> print(chr(ord('{')-26))
'a'

So the target cookie is nqzva. Modify the cookie on Browser Dev-tools and refresh the page to get the flag.

flag{H4cK_aLL_7H3_C0okI3s}