Cracking root user: Automating logging into root using "su" from nonroot user

Question

I want to write a script that allows me to pass a password to the su command. The reason for this is to automate the process of logging into root from nonroot account. From my basic understanding of security, I know the dangers of this. I still need this to try to crack the root user password by reading passwords from a file.

I have heard about using the expect command to automate interactions but I do not know how it works, or if it is applicable in this situation. Any information about using expect would be greatly appreciated.

Please note that sudo is not an option as my user is not on the sudoer list.

Things I've tried - Passing the password in using pipes Didn't work because of "su must be used from terminal" type error - Passing the password using echo Whatever was echoed would simply show up after the password was entered

Answer 1

Doing this "oneline style"

expect -c 'spawn su - ;expect Password:;send "your-password\n";interact'

Take a look at the output of su - to guarantee if this is the right phrase that appears to capture a password. I'm using a translated version of Linux here so, the word would be "Senha:" instead of "Password:".

• expect -c '': Run the following actions to this command
• spawn su -: Execute this command
• expect Password: Expect the word password to do something
• send "your-password\n": Type in your password, followed by an Enter
• interact: Keep interaction ready to the command.

Answer 2

You can use expect to do that job for you. Save the following to a file, make it executable, and run it:

#!/usr/bin/expect
spawn su
expect "Password:"
send "YOUR_PASS\n"
interact

(Obviously, you need to specify the correct path to expect. Here I used /usr/bin/expect as an example.)

If YOUR_PASS is the correct root password, you should now have a root shell. If not, you get an authentication failure.

Note that the interact command will probably not be needed in the context of a fully automated script, as it gives control of the process to the user, i.e., keystrokes are sent to the current process and stderr and stderr are returned.

See man expect for a more detailed description of the commands spawn, expect, send and interact, and many other commands.