How To Do Linux Privilege Escalation: Using SSH Identity Files
Part of Linux privilege escalation is finding leftover SSH RSA keys. A lazy admin can leave them unprotected and readable and therefore we can use them to connect to the target using the SSH ID files. These are the RSA private keys created when a private key, public key pair is generated for a user.
This is a classic technique you should know how to do if you want to PASS THE OSCP or BECOME AN ETHICAL HACKER.