Sharky CTF 2020 Writeup | Web

Jai Gupta
3 min readMay 12, 2020


Sharky CTF 2020 Walkthrough for web category —


One of your customer all proud of his new platform asked you to audit it. To show him that you can get information on his server, he hid a file “flag.txt” at the server’s root.

The name of the challenge clearly suggest that the challenge is related to XXL injection, to find out the content of file /flag.txt

Stored data look strange, and it shows requesting some XML file in the URL. If we add some garbage to the query string, like ?xml=jhvhjvvvkvkj, a bunch of errors is spat out of the application showing some of the functions used in web apps.

Now finding some XXE payload that can show the content of flag.txt Here is the Sample..

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE foo [ <!ENTITY xxe SYSTEM "file:///flag.txt"> ]>

Now since there is no submit option to upload our payload to the server, we need to create a link that can be used to forward the code to this website server. Here I have used to upload the code. Use that link in the URL to get the flag..

Flag- shkCTF{G3T_XX3D_f5ba4f9f9c9e0f41dd9df266b391447a}

Logs In ! Part 1

Data printed on one of our dev application has been altered, after questioning the team responsible of its development, it doesn’t seem to be their doing. The H4XX0R that changed the front seems to be a meme fan and enjoyed setting the front. We’ve already closed the RCE he used, there is a sensitive database running behind it. If anyone could access it we’ll be in trouble. Can you please audit this version of the application and tell us if you find anything compromising, you shouldn’t be able to find the admin session. The application is hosted at logs_in

The description tells of finding the admin section on the page. This was really an easy challenge if you navigate to the correct link. The link to the admin section or say the flag lies at the footer of the page. Clicking on MainController::index in the Request/Response screen revealed some routes:

The route is highlighted on the debug page.

Opening the link takes us to the admin page or the flag.


Thanks for your patience, I hope you enjoyed reading. Happy Hacking...

Originally published at Sharky CTF Writeups on May 12, 2020.



Jai Gupta

Build & Break | OSCP | Red Teaming | Penetration Testing