Concepts to consider

only this, from the manual

diff (1)             - compare files line by line

bandit 17

Task

There are 2 files in the homedirectory: passwords.old and passwords.new. The password for the next level is in passwords.new and is the only line that has been changed between passwords.old and passwords.new

NOTE: if you have solved this level and see ‘Byebye!’ when trying to log into bandit18, this is related to the next level, bandit19

Solution

bandit17@bandit:~$ diff passwords.new passwords.old 42c42 < hga5tuuCLF6fFzUpnagiMN8ssu9LFrdg

p6ggwdNHncnmCNxuAt0KtKVq185ZU7AW

That is the password for the next level but as we see it comes out byebye ending the connection. This is because the .bashrc has been modified to log me out