How to Disable Telnet access on server
Telnet should be disabled on all web servers, and you should use SSH which is more secure.
Telnet sends password in plain text passwords and usernames through logins, and
‘crackers/hackers’ can obtain these passwords easily as compared to SSH.
TELNET server listens for incoming messages on port 23, and sends outgoing messages to port 23.
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.