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Wily_One
Premium Member
join:2002-11-24
San Jose, CA

1 recommendation

Wily_One to treich

Premium Member

to treich

Re: how do I disable people telneting into my mail server

First of all, if you are really telnetting into your system you should disable telnet altogether and use SSH.

As for port probing, which is what this is, you can't do much to prevent it. You can block repeat offenders with something like iptables.

graysonf
MVM
join:1999-07-16
Fort Lauderdale, FL

graysonf

MVM

Telnet, in the context of this thread, refers to using a telnet client to connect to a TCP service port, not the insecure practice of telnetting to to a telnetd daemon for shell access.
dave
Premium Member
join:2000-05-04
not in ohio

dave to Wily_One

Premium Member

to Wily_One
telnet clients can be used as a way to make a TCP connection to any TCP port, and then send bytes on that connection. In this sense, the telnet client is simply a handy program to copy bytes from keyboard to TCP connection.

Whether you can operate the protocol that the server is expecting depends on your own skill - e.g. whether you can type SMTP on-the-fly and generally without recourse to a delete key.

graysonf
MVM
join:1999-07-16
Fort Lauderdale, FL

graysonf

MVM

LOL. Never tried the delete key Backspace doesn't work either

leibold
MVM
join:2002-07-09
Sunnyvale, CA
Netgear CG3000DCR
ZyXEL P-663HN-51

leibold

MVM

Some telnet clients use line buffering which allows the backspace key to work as expected (since the correction takes place before the data is send to the server).

It is amazing how frequently that backspace key is being used subconsciously. I can remember times when a quick telnet test didn't work as intended only to find a ^h or \008 in the server side log files

graysonf
MVM
join:1999-07-16
Fort Lauderdale, FL

graysonf

MVM

Yes, a client I use once in a while has a type ahead box you can stuff the whole line in, and it all sits there capable of being corrected until the Enter key is pressed. But I rarely use it. For me it's easier to spawn the session in shell and live with the occasional mistake.

Wily_One
Premium Member
join:2002-11-24
San Jose, CA

Wily_One to graysonf

Premium Member

to graysonf
Was there anything in my post that made it sound like I didn't know that? I telnet to specific ports all the time to verify the firewall is not blocking it.

User complaining about port probes. Then people go on a tangent about him knowing or not knowing how to telnet into his own server. That is the context for my comment about that not being a good idea. Use SSH for server access, not telnet.

Keep using telnet for server access - I don't give a shit. LOL