picobrowser

The webpage looks like this.

Clicking on the green Flag button returns this.

It shows the User-Agent header.

In case you don’t know what a User-Agent header is, it’s a piece of information your web browser sends to website to identify itself.

It tells what browser and OS your using, so the website adjusts its content to work best for you.

You're not picobrowser! Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36

I’m currently using 64 bit Windows 11.

Clicking on the Sign In and Sign Out button This isn’t implemented yet.

It looks like the challenge wants us to change the User-Agent header.

I don’t think you can change the User-Agent header in the browser unless your using a sophisticated browser like Firefox.

I’m using Brave and there isn’t an option.

Instead you can use the Python’s requests module to change the User-Agent header.

import requests

headers = {"User-Agent": "picobrowser"}

res = requests.get(
    "https://jupiter.challenges.picoctf.org/problem/28921/flag", headers=headers
)
print(res.text)


# <code>picoCTF{p1c0_s3cr3t_ag3nt_84f9c865}</code></p>

It’ll give you the the flag.

You can also use curl.

The -A option allows you to set the User-Agent.

curl -A "picobrowser" https://jupiter.challenges.picoctf.org/problem/28921/flag | grep -o picoCTF{.*}