ctf-writeup/DeadSec CTF 2023/Bing

Bing

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About the Challenge

We have been given a website that contains a form and we can input a host there

And then I tried to input 127.0.0.1 and here was the output

How to Solve?

We need to exploit the website using Command Injection vulnerability in order to read the flag. Here is the payload I used to read the flag

127.0.0.1;c\a\t${IFS}/f\lag.txt${IFS}|base64

Because some of the commands are blacklisted by the website (Like cat or ls), we can trick it with / character. And because whitespace is also blacklisted by the website we can use ${IFS}

dead{okokok!!!_th1s_flAg_f0R_Y0U}