Practitioner Lab 9: Web shell upload via extension blacklist bypass

 

This lab contains a vulnerable image upload function. Certain file extensions are blacklisted, but this defense can be bypassed due to a fundamental flaw in the configuration of this blacklist.

To solve the lab, upload a basic PHP web shell, then use it to exfiltrate the contents of the file /home/carlos/secret. Submit this secret using the button provided in the lab banner.

You can log in to your own account using the following credentials: wiener:peter

to start this lab I logged in as wiener





This lab took me longer than I wanted. I didn’t understand how .htaccess worked very well but After doing some research I learned how it all worked and how it gives configurations for a particular directory.



I knew it was an apache server because when I first did the post request it told me it was apache.

I went and made an .htaccess file



This file basically tells the server that if it sees any .php5 to then run that file as if it was a php file.

When I initially uploaded this I made the mistake of uploading it using the ../ because I thought it needed to be in the previous directory. But after doing more research I found out that it needs to be in the same directory.



Here I am uploading the .htaccess file with the rule.



Here I uploaded a .php5 file that would then be executed by the server as if it was a php file.



I then saw this request which I used to execute the script. I sent this to repeater and there I executed the script



Here the content was executed correctly and I got the flag



The lab is now Done.

I found this lab pretty tricky simply because even though I knew about .htaccess I didn’t fully understand how to use it. But now I have learned and hopefully won’t struggle as much with these labs.

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