Sometimes you will try all the methods mentioned above, but some web sites are really secure and there is no easy way to exploit them.
Often this doesn’t stop us from hacking them, they might have open ports running some services such as, ftp, telnet and so on, try to brute force it and get the password, Hydra is another amazing tool for this kind of tasks.
If you have a physical access to the server you get everything in your hands, be discrete and leave a backdoor on it and you done.
Other Kind of Attacks You Can Also Perform Are:
Buffer Overflow Heap Overflow Integer Overflow
And the list is long, i just shared what i got now in my mind, you can also add yours in the comments sections…