Reading and writing files on the server

In this section, we will look at how we can use SQLi to read any file in the server. So, even if the file exists outside the /www directory, we'll be able to read it exactly as with a file-disclosure vulnerability, and we'll see how we can use it to write files and upload them to the system, just as with a file-upload vulnerability.

First, let's take a look at reading the file; we are going to set everything to null. So, our statement is going to be as follows:

union select null,load_file('/etc/passwd'),null,null,null

Instead of selecting a column or a table, we want to run a function called load_file(), and we are going to set the file that we want to load. We're going to use the same file that we had a look at in the file-inclusion vulnerability, which was /etc/passwd. The URL command is as follows:

index.php?page=user-info.php&username=zaid' union select null,load_file('/etc/passwd'),null,null,null%23&password=123456&user-info-php-submit...