This is a Linux machine with SSH and Web services enabled, we notice strong hints on the homepage that we need to perform base64 encoding. After base64-encoding the wordlist used for web enumeration, we obtain an encrypted SSH private key. Using john the Ripper along with the password hint on the homepage(requiring base64 encoding), we quickly obtain the decryption key and gain a foothold on the system.

Then we discover that the initial user-configured sudo rules allow us to exploit the base64 utility to read arbitrary files, thereby obtaining the root user's SSH private key and gaining full system privileges.