Chocolate (Web Exploitation) – 50

Description

If you could become admin you would get a flag. Link

Solution

Looking at the HTTP header for the site, we see a cookie being exchanged.

It has this value.

e2FkbWluOmZhbHNlfQ%3D%3D

Which when decoded from URL format gives us

e2FkbWluOmZhbHNlfQ==

Aha, now doesn’t this just look like base64. Decoding it gives us,

{admin:false}

So, let’s change it to

{admin:true} then re-request the page.

e2FkbWluOnRydWV9 is our new cookie value.

We can use the chrome dev console to change the value of our cookie.

document.cookie="coookie=e2FkbWluOnRydWV9"

Refresh the page and we get our flag

ABCTF{don’t_trust_th3_coooki3}

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