Challenge Description#

backup my index pls

Analysis#

Because there was no URL given for the challenge instance, I initially thought the target was the CTFd site itself. The hint “backup my index” strongly suggests a leftover backup file such as .bak, .old, or .swp.

Exploitation#

Access the backup file directly:

curl https://ctf.sriwijayasecuritysociety.com/index.php.bak

The response contained the flag directly inside the HTML:

<main role="main">
    <div class="container">
        <p>SCSC26{4h_1_f0rg3t_to_d3letE}</p>
    </div>
</main>