How to block FTP ,SMTP,Telnet services?


 
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Top Forums UNIX for Dummies Questions & Answers How to block FTP ,SMTP,Telnet services?
# 1  
Old 09-08-2010
How to block FTP ,SMTP,Telnet services?

My distribution details.
Code:
# lsb_release -a
LSB Version:    :core-3.1-ia32:core-3.1-noarch:graphics-3.1-ia32:graphics-3.1-noarch
Distributor ID: EnterpriseEnterpriseServer
Description:    Enterprise Linux Enterprise Linux Server release 5.2 (Carthage)
Release:        5.2
Codename:       Carthage

Code:
# uname -a
Linux TomcatServer 2.6.18-92.el5 #1 SMP Fri May 23 22:17:30 EDT 2008 i686 i686 i386 GNU/Linux

I would also like to know if i can disable the service instead of blocking the port.

I m reffering to following link which explain how to disable the service.
Hardening Linux Servers - Forums
Quote:
1. To disable Telnet, you must edit the /etc/xinetd.d/telnet file. Open the Telnet file, using vi or an editor of your choice.
2. Comment out the service telnet line by adding a number sign (#) before service telnet: #service telnet
3. Write and quit the file.
I m not able to get telnet file under /etc/xinetd.d/

So i m stuck please help.
# 2  
Old 09-08-2010
Not knowing your distribution, you can still be using inetd instead of xinetd. So maybe have a look if there is a /etc/inetd.conf and comment it out. It could also been started as standalone demon, not being called by a super demon like inetd or xinetd. In that case (I doubt it) it could be started somewhere in /etc/rc.d/rc.<n>.

You can check what super demon you are currently using if you just issue a
Code:
ps -ef| grep inetd

and you will notice which of both you are using.

When commenting anything out in either config, don't forget to refresh/restart the super demon.

If you are definetly using xinetd and there is no config file containing a stanza for telnet below /etc/xinetd.d, then you might just not using telnet. Did you just try to connect with a telnet client to your server and check what happens?
# 3  
Old 09-08-2010
Quote:
Originally Posted by zaxxon
Not knowing your distribution, you can still be using inetd instead of xinetd. So maybe have a look if there is a /etc/inetd.conf and comment it out. It could also been started as standalone demon, not being called by a super demon like inetd or xinetd. In that case (I doubt it) it could be started somewhere in /etc/rc.d/rc.<n>.

You can check what super demon you are currently using if you just issue a
Code:
ps -ef| grep inetd

and you will notice which of both you are using.

When commenting anything out in either config, don't forget to refresh/restart the super demon.

If you are definetly using xinetd and there is no config file containing a stanza for telnet below /etc/xinetd.d, then you might just not using telnet. Did you just try to connect with a telnet client to your server and check what happens?
Code:
# ps -ef| grep inetd
root      4523     1  0 16:28 ?        00:00:00 xinetd -stayalive -pidfile /var/run/xinetd.pid

Being a new user to linux i m finding it very difficult to understand what do you mean by "So maybe have a look if there is a /etc/inetd.conf and comment it out."

I guess in my case i dont want to comment it out as i m having xinetd configured in my system thanks to "ps -ef| grep inetd" command given by you.
Can any one please help me out by telling what should i do to block following services respectively.
1)Telnet
2)FTP
3)SMTP
Please dont suggest blocking the port.
# 4  
Old 09-08-2010
Quote:
I guess in my case i dont want to comment it out as i m having xinetd configured in my system thanks to "ps -ef| grep inetd" command given by you.
Ok, then no need to worry what I wrote about inetd.

It could simply be the case, that your xinetd is just not configured for telnet and ftp.
Type in
Code:
find /etc -name "xinetd*"

and post the output please.

Also do following to make sure:
Type in from the same box or another PC, server, whatever (even Windows) at some command line:
Code:
telnet <ip-address or hostname of host to be hardened>
ftp <ip-address or hostname of host to be hardened>

If you get no login prompt but an error message for telnet as well as for ftp, we don't have to investigate further.

For smtp, we have to checkout what message transfer agent (MTA) you are using. Type in following:
Code:
ps -ef| grep -iE "sendmail|postfix|exim|courier|james|lotus|qmail|xmail|postmaster"

And post the output please.
This User Gave Thanks to zaxxon For This Post:
# 5  
Old 09-08-2010
Quote:
Ok, then no need to worry what I wrote about inetd.

It could simply be the case, that your xinetd is just not configured for telnet and ftp.
Type in
Code:
find /etc -name "xinetd*"

and post the output please.
Code:
# find /etc -name "xinetd*"
/etc/xinetd.d
/etc/rc.d/init.d/xinetd
/etc/xinetd.conf
/etc/sysconfig/xinetd


Quote:
Also do following to make sure:
Type in from the same box or another PC, server, whatever (even Windows) at some command line:
Code:
telnet <ip-address or hostname of host to be hardened>
ftp <ip-address or hostname of host to be hardened>

If you get no login prompt but an error message for telnet as well as for ftp, we don't have to investigate further.
Code:
# telnet localhost
Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
telnet: Unable to connect to remote host: Connection refused

I guess its not running on my machine any way i m able to ssh to the server.How would i block ssh then?

Quote:
For smtp, we have to checkout what message transfer agent (MTA) you are using. Type in following:
Code:
ps -ef| grep -iE "sendmail|postfix|exim|courier|james|lotus|qmail|xmail|postmaster"

And post the output please.

Code:
# ps -ef| grep -iE "sendmail|postfix|exim|courier|james|lotus|qmail|xmail|postmaster"
root      4598     1  0 16:28 ?        00:00:00 sendmail: accepting connections
smmsp     4615     1  0 16:28 ?        00:00:00 sendmail: Queue runner@01:00:00 for /var/spool/clientmqueue

What about FTP service?
# 6  
Old 09-08-2010
Yes, it seems telnet is not active and the config for xinetd is not installed.
To make sure you can show the contents of /etc/xinetd.d. If there is a file called telnet and one called ftp, you can check inside them - there should be a parameter called "disable" which might be already set to "= yes".

For ftp I already mentioned to do the same as with telnet - you might have overlooked it:
Quote:
Also do following to make sure:
Type in from the same box or another PC, server, whatever (even Windows) at some command line:

Code:

telnet <ip-address or hostname of host to be hardened>
ftp <ip-address or hostname of host to be hardened>

Your MTA is sendmail - check if there is entries in /etc/rc.d/rc.<n> where <n> is the appropriate run level.
There are links pointing to the start/stop script for sendmail most probably. Those containing a S are for start and those with a K are for stopping/killing it. Just remove the links for sendmail so it will neither be started or stopped.
Some distributions of Linux have a tool called a graphical "run level editor" (SuSE) to change those entries (enable/disable etc.) or something like chkconfig for command line. Debian has update-rc.d for example - no clue what your distribution uses. But manually removing the links as described above should work.
# 7  
Old 09-08-2010
During this learning phase i came across a strange problem.

I was just checking the configuration file of /etc/xinetd.d/krb5-telnet and i thought of enabling the telnet.
I modified the configuration file accordingly and restarted the server.
Code:
# cat /etc/xinetd.d/krb5-telnet
# default: off
# description: The kerberized telnet server accepts normal telnet sessions, \
# but can also use Kerberos 5 authentication.
service telnet
{
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/kerberos/sbin/telnetd
log_on_failure += USERID
disable = no
}

Now i can able to telnet to the server from any other machine But the problem is it is not allowing me to login with correct root credentials.

What could be the issue here?

I m able to login with ssh protocol.
 
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