ctf-writeup/CyberSecurityRumble Quals/ChapGPyT

ChapGPyT

I've made ChatGPT implemented a challenge. I hope you can solve this verry hard challenge

About the Challenge

We were given a website to test and this website only have 2 endpoints. First is /post_message where we can input our message and then in the response we got some random string. Here is the HTTP request and response when I tried to send a random message using /post_message endpoint

And then the second endpoint is /get_message/$id. We need to input the output from the /post_message endpoint into the $id. So for example /get/message/df8311b35d02df17fb4d644e313b1a62

Our input will be reflected in the response

How to Solve?

At first, i got stuck for so long because i already tried some web exploitation such as Arbitrary File Upload, SSTI, etc. And then I tried to search the random string in google and also tried to crack the random string, it turns out that is a number that has been hashed using MD5

Now, I tried to check another message with id c4ca4238a0b923820dcc509a6f75849b. That hash is equivalent to 1

CSR{GrindingChatGPTUntilItGivesYOuAChallangeLol}