Telnet sends clear text passwords and usernames through logins and should be disabled on servers and replaced with SSH.
Enabling telnet is a great security risk to your servers. It should be turned OFF on servers to avoid any further exploits. TELNET server listens for incoming messages on port 23, and sends outgoing messages to port 23.
Follow the steps given below to disable telnet on server.
1. Login to your server through SSH and su to root.
2. Type pico /etc/xinetd.d/telnet
3. Look for the line: disable = no and replace with disable = yes
4. Now restart the inetd service: /etc/rc.d/init.d/xinetd restart
5. Turn off it through chkconfig as well because it can still start through that.
/sbin/chkconfig telnet off
6. Scan your server to ensure port 23 is closed.
nmap -sT -O localhost
Also run ps -aux | grep telnet and if you find anything other than “grep telnet” as result kill the process.