ctf-writeup/b01lers CTF 2023/warmup

warmup

My first flask app, I hope you like it

About the Challenge

We have been given a website without source code

How to Solve?

If we check the source, code there is another endpoint called debug.html

And if we decode aW5kZXguaHRtbA== we will get index.html. Now change it from index.html to debug.html and encode it with base64

Now we got another file called app.py. Now, try to access app.py endpoint (Dont forget to encode the name again)

As you can see the flag is located in flag.txt endpoint. But we can't access it directly because there is a function called validate to detect if our input is flag.txt or not

def validate(data):
    if data == b'flag.txt':
        return True
    return False

To bypass that, we need to add ./ on the endpoint. For example from flag.txt to ./flag.txt. And then repeat then encode the endpoint again with base64 and you will get the flag

bctf{h4d_fun_w1th_my_l4st_m1nut3_w4rmuP????!}